I'd suggest Badwater Basin. When I was a new to TF2 I played the Badwater tonnes, because I absolutely loved the map, and it was very easy to get into. And I know another person who did this too, so I'd say it's a pretty good map for new players.

When I first started, I played the crap out of Dustbowl and 2fort, which are two very simple maps in my opinion :3

2fort for sure.

2fort is a great map

2Fort is way overrated. 
 
Try a payload map. Gravelpit is probably the best CP map. Turbine is also good to learn Engineers.

2Fort is great.
 
Awesome practice at whatever.

There's no one map that's good for beginners but they're all easy to learn if you play them for a while. My personal favourite maps are Turbine, Badwater Basin and Dustbowl.

2fort was designed to display the strengths of every class.
 
But really, you can experiment on almost any map.

play them all.

The payload maps (the ones where you push a cart like Goldrush or Badwater Basin) have the simplest and, more importantly, most approachable mechanic in TF2. If you are on the BLU team, you need to stand next to the cart. If you are on the RED team, you need to keep people away from the cart. The gameplay is focused and simple. 
 
Why are people recommending 2Fort, for the nostalgia factor? CTF has never been TF2's strong suit and too many shenanigans between Snipers and Engies occur on that map for it to be good for a newbie.

" The payload maps (the ones where you push a cart like Goldrush or Badwater Basin) have the simplest and, more importantly, most approachable mechanic in TF2. If you are on the BLU team, you need to stand next to the cart. If you are on the RED team, you need to keep people away from the cart. The gameplay is focused and simple.  Why are people recommending 2Fort, for the nostalgia factor? CTF has never been TF2's strong suit and too many shenanigans between Snipers and Engies occur on that map for it to be good for a newbie. "

2fort is a really good map to learn and develop skills that, while not necessarily required, make the game a lot more fun and satisfying. This is because 2fort normally ends up being nothing more than team deathmatch, so you are able to concentrate pretty independently on not dying, as opposed to the objective of most other maps.

" @MattyFTM said:

" I'd suggest Badwater Basin. When I was a new to TF2 I played the Badwater tonnes, because I absolutely loved the map, and it was very easy to get into. And I know another person who did this too, so I'd say it's a pretty good map for new players. "

Not sure if Matty is referring to me or not, but I totally did this. That map is insanely fun because of the different routes, methods of playing and the wide, open space. If I were you though, I'd just go in to a map rotation server and see what takes your fancy. "

2Fort or Dustbowl.

Having FINALLY played the game...2Fort.  Great map.