I've not played all that much of the online but so far it looks like most of the people are rocking the great sword and the blade&shield. I've seen some switch axe users as well and a couple of hammers but not as many compared to the great swords and blade&shield users. I've only met one guy who used the long sword but that must be because you only unlock the longsword later in the single player campaign. Bowgun users and lancers seem to be completely absent which makes me feel  that i look a bit like an odd duck since i rock a lance that looks like a remote lightning antenna. Well it might also be because i have a Jaggi Head hat ^^ 
 

All of the folks I play with either use the LS or the GS. A couple use SnS.

It seems like every team I join will always have a Great Sword and SnS , the final space usually being a Longsword. Can't say I've seen many Lances and bowguns, Xeiphyer is certainly right about the price.
I feel very alone as a Hammer hunter, slowly working on his Iron Striker.

Nice Jaggi head by the way, I've grown quite attached to my Barroth helm myself.

I'm mostly seeing Greatswords, Longswords, Lances & Switch Axes. Bowgunners are extremely rare, and both SnS and Hammer users seem a bit uncommon.
 
I've pretty much used nothing but Greatswords so far, with a Focus + Critical Draw armor set. Might make some Lance sets soon and start using those too.

I've always seen some hammer user around but them along with gunners get knocked out more often than any other weapon user.  The GS and LS and SA make up the majority at HR40. I've seen enough hammers, lancers around too. Gunner is rare as usual, which is obvious because even I can't wrap my head around making a good gun combination, let alone shoot with it.
 
The primary weapons I make are the GS, LS and Hammer. Though I see myself using the GS and LS more often due to their 'party friendliness'.
 
The hammer requires some careful super slam placements to not smack other players around. I find myself considering the position of other hunters more than the monster, which takes out the fun of  KOing the monster a bit. (Only a little bit, KOs are always satisfying)
 
The GS just needs to not use the upswing, and the LS might trip up people when doing the spirit combo but generally other players don't suffer too much. I find a lot of lancers smacking me away from the action with their charge though. They do it when the monster tripped, totally taking away my chance at some free hits.
 
SnS... Well, I'm always wondering if they do enough DPS. I find the hunts last longer when there's an SnS in the group. I prefer to have none.
 
Anyways at HR40 I see a lot more SA users than before, which I find getting knocked out as often as the hammer and gunners. They do a lot of damage though, fights go pretty fast with them around.

" The GS just needs to not use the upswing, and the LS might trip up people when doing the spirit combo but generally other players don't suffer too much. I find a lot of lancers smacking me away from the action with their charge though. They do it when the monster tripped, totally taking away my chance at some free hits.  "