Ever since Pokemon Blue, I've always chosen grass Pokemon for my starter, and later on my team. This was partially because I liked the color green, and partially because grass was good against the first two gym leaders, Brock and Misty. This tradition carried on until now where I chose Snivy as my starter, and it's been nothing but torment throughout.  
 
First, let's look at the base stats of the fully evolved starters (taken from bulbapedia): 
 
Serperior (grass)
 
HP: 75
Attack: 75
Defense: 95
Special Attack: 75
Special Defense: 95 
Speed: 113 
 
Emboar (fire)
 
HP: 110
Attack: 123
Defense: 65
Special Attack: 100
Special Defense: 65 
Speed: 65 
 
Samurott (water)
 
HP: 95
Attack: 100
Defense: 85
Special Attack: 108
Special Defense: 70 
Speed: 70 
 
Although the stat totals are the same, the utilities are not. 
 
Serperior is much faster than either of the other two starters; but the thing is, he's so redundantly fast that he's faster than almost every other Pokemon out there (even electric and flying Pokemon). What could've been extra offense or HP becomes wasted stat points. 
 
Due to having a better defensive advantage over the other two starters, he's grossly lacking in the offensive department. Anyone who's played the Pokemon games knows that it's better to defeat your opponent's Pokemon in one blow than to get hit and weather their counterattack, no matter how high your defense. This disadvantage means that despite Serperior's "superior" defensive skills, in the end he takes more damage than his counterparts.  
 
More importantly are the skewed matchups in the game. Not only have grass weaknesses like Poison and Bug been hugely buffed (the days of roflstomping Caterpies and Weedles are gone apparently), but the game specifically pits you against grass weaknesses all throughout.  
  
Pokemon League: 

Gyms
 
1. Grass/Fire/Water Type; Disadvantage to All (always pits you against opposite of your starter) 
2. Normal Type; Neutral 
3. Bug Type; Disadvantage to Grass, Advantage to Fire, Neutral to Water 
4. Electric Type; Advantage to Grass, Neutral to Fire, Disadvantage to Water 
5. Ground Type; Advantage to Grass, Disadvantage to Fire, Advantage to Water 
6. Flying type; Disadvantage to Grass, Neutral to Fire, Neutral to Water 
7. Ice Type; Disadvantage to Grass, Advantage to Fire, Neutral to Water 
8. Dragon Type; Disadvantage to all
 
So in the gym matchups, Grass is disadvantaged in 5/8 gyms, Fire 3/8 gyms, and Water 3/8 Gyms.  
  

How about Elite 4?  
 
Shauntal (Ghost): Most of her Pokemon have some sort of poison, ice or fire attack. On the other hand, there is only one single electric move and one single water move.   
Grimsley (Dark): Flying, poison and bug attacks are all abundant. Ground and rock attacks are also abundant here for a change, and there is one electric move.  
Caitlin (Psychic): Flying and ice are both present here, but the focus is on electric attacks 
Marshal (Fighting):  Plenty of bug, flying and poison here, but also lots of ground, rock and grass. Fairly even weaknesses throughout but grass weakness still the strongest.

Although the Elite 4 exploit the weaknesses of all the starter Pokemon, grass gets its weakneses exploited the strongest and most often.  
 
Now let's consider the legendary dragon trio: 
 
Reshiram: Fire/Dragon 
Zekrom: Electric/Dragon 
Kyurem: Ice/Dragon 
 
Grass: 2 Weaknesses 
Water: 1 Weakness 
Fire: None 
 
Grass comes out last once again.  
 
My final example, and the one that illustrates my point best, is the battle with the Champion, Alder. They didn't even try to hide the disparity with this one: 
 
Accelgor (Bug): with Bug Buzz, a very powerful bug-type move.
Bouffalant (Normal): has the ability Sap Sipper that first cancels any Grass-type move and then boosts its own stats - all automatically. You'd think there'd be some equivalent handicap ability to accommodate Fire and Water on his other Pokemon; nope. Also has the Bug move Megahorn, which can one-hit KO my lvl 100 Serperior. 
Druddigon (Dragon): resistant to Grass, Fire and Water, but has an ability that punishes contact moves. Guess which type has the most contact moves?  
Vanilluxe (Ice): ice type with Blizzard move.  
Escavalier (Bug/Steel): its type provides quadruple resistance to Grass type, and in addition it packs X-Scissor, another powerful Bug type move. And for some reason Aerial Ace too, a Flying move (even though the Pokemon is an insect covered in knight's armor). 
Volcarona (Bug/Fire): quadruple resistance against Grass again, and a Fire move (Overheat) that will one-hit KO most grass types, with Bug Buzz to finish the job. 
 
It's like the Champion was specifically designed to rape grass type and nothing else. 
 
I beat the game under these conditions, but it wasn't pleasant. I hope to see a change to this type discrimination in later games.
 
TL;DR 
 

All of them have been. They have all ways favored Fire type pokemon .

All of them have been. They have all ways favored Fire type pokemon .

Grass is generally accepted as one of the worst types in the game, next to poison. It is mostly due to type disadvantages both offensively and defensively. Furthermore, in general the stats of many fully evolved grass types are...middling at best. However, that isn't to say that grass doesn't have its pluses, but there are serious disadvantages. There are plenty of good offensive grass types, such as Sceptile and Leafeon, but the problem with grass STAB moves are that many resist there attacks, and the strongest grass moves generally have some drawbacks. In addition, many grass types need weather to set up, which usually takes a turn to do. Furthermore, the most common offensive moves and pokemon have the ability to use fire and ice moves, which are super effective against most grass types.

That said, grass is still very effective against water types (the most common type in game and in the metagame) and doesn't have the crippling problems that electric types have against ground types. Plus they also resist the ever annoying ground moves (i.e. earthquake), but only the non-poisons resist it (which there are a good number that are both poison and grass....a bad STAB combination).

That's cause Grass types suck ass.

That image... it's magical.

All of them have been. They have all ways favored Fire type pokemon .

 I too always pick the grass guy but wind up ditching my starter halfway through the game. Mix it up a bit.

@JJOR64 said:

@The_Laughing_Man said:

All of them have been. They have all ways favored Fire type pokemon .

Emboar is fucking garbage.

You shut your whore mouth

The legendary plant Poke in b/w is one of the more useful legendaries other than the ice dragon which is just goddamn ridiculous. Make it part dragon, then make it immune to its one weakness. 
But I disagree. I feel like B/W heavily favor water types over anything else, and flying. And then there's everything else, and then bug in dead last where it belongs along with steel. There is no "redundantly fast" because if you're not faster than most flying types, you'll get fucked. Swanna's fucking god tier aight.

I hate grass type pokemon, always gotta go fire!

@ryanwho: Water types have always been one of the best types in the entire game due to their good coverage. They are generally at least neutral to most type combinations, and defensively can at least take some of the hardest hitting moves in the game. The good thing about B/W is that they didn't add another million unnecessary water type pokemon and decided to spread the love a little more.

But your statement about flying types makes no sense to me, flying types hasn't NEARLY gained as much this generation as Bug has, mostly due to the addition of a lot of new good bug types (Volcarona, Galvantula, and Accelgor) and the move Quiver Dance. Also, Swanna has awful stats and is only best played when set up by another pokemon, which in this fast metagame is just too many turns to do.

@Enigma777 said:

That's cause Grass types suck ass.

This man knows what's up!

@yoshimitz707 said:

@Enigma777 said:

That's cause Grass types suck ass.

This man knows what's up!

Fuck ya he does.

@JJOR64 said:

@The_Laughing_Man said:

All of them have been. They have all ways favored Fire type pokemon .

Emboar is fucking garbage.

You shut your whore mouth

That's cause Grass types suck ass.

Really not much to choose from as far as fire types this gen. Maybe because one of the story legendaries is part fire type, idunno. But if you're looking for a fire type with high sp attack, you gotta look at another gen. @neoepoch said:

@ryanwho: Water types have always been one of the best types in the entire game due to their good coverage. They are generally at least neutral to most type combinations, and defensively can at least take some of the hardest hitting moves in the game. The good thing about B/W is that they didn't add another million unnecessary water type pokemon and decided to spread the love a little more.

But your statement about flying types makes no sense to me, flying types hasn't NEARLY gained as much this generation as Bug has, mostly due to the addition of a lot of new good bug types (Volcarona, Galvantula, and Accelgor) and the move Quiver Dance. Also, Swanna has awful stats and is only best played when set up by another pokemon, which in this fast metagame is just too many turns to do.

@JJOR64: Emboar thrives in Trick Room, with Reckless and high HP it can do massive damage. Especially since it has access to head smash, wild charge, and flare blitz. That said, without a trick room Infernape and Blaziken outclass it completely.

@ArbitraryWater: Sceptile actually has a fairly diverse moveset, A Choice specs, timid, max speed, special attack with energy ball (or leaf storm), dragon pulse, focus blast, and HP Ice (or fire) is a good sweeper. Also, Venusaur got Chlorophyll this generation which makes it a fairly potent threat in the sun.

@ryanwho: ...Water/Flying is a generally not a good typing. It is 4x weak to electric, which is a very common type (or its moves are seen a lot). The only on who actually can do this typing justice is Gyarados, because of its fantastic movepool and access to dragon dance. Also stats DO in fact matter, especially when none of its stats break 100. It may have 98 base speed, which outspeeds Gyara, but it doesn't have the offense or defense to back it up without serious set up or support. Contrast with Gyara with its massive attack and sp.def and the hp the moves to back that up.

Fighting types had gotten a boon this generation due to 'mons, like Conkeldurr, Scrafty, Meinshao, and the fighting legendaries. The addition of those types, and their commonality in the metagame have actually caused psychics to increase in usage (something that hasn't been seen in a long time)

Im not using fighters correctly I guess. It seemed like my fighting legendaries were getting killed by goddamn everything.

@ryanwho: It may be a nature thing. Although most people, will say ingame it doesn't really matter (and it doesn't USUALLY) a hindering nature will actually cause significant performance problems. Because nature increases one stat by 10% and decreases one stat by 10%. Also, it depends on the moveset you are using, and who they are going up against. Cobalion, and Virizion can take some (neutral) hits, but Terrakion is slightly more fragile. Also, Virizion and Terrakion have a large number of weaknesses, which means you got to get them in on a safe switch, cause their speed is enough to be alright.

These games aren't designed to be played with only one type of pokemon.

Grass Type is my favorite type, and my least favorite is probably Fire. Grass has a disadvantage in resists, however move sets aren't bad, and the designs are awesome. With Fire and water type being overly popular, I think grass type Pokemon didn't what they deserved

@nickl Meh, Fire type is overrated. I hate Fire type probably more than you hate grass lol.