there's 3 sets of armor at the top tier of gear, which is PvE gear gotten from PvE only, Bounty Hunter gear which is PvE/PvP gear gotten from both, and PvP gear gotten from PvP.
Gear matters little tho, unless if you are 1v1 fighting an equally skilled peep, which will almost never happen. Being smart/playing your class well > gear if you can outplay the other guy.
All those separate types do is not much. PvE gear is more defense oriented, PvP gear is more offense oriented, Bounty Hunter is a mix of both.
EDIT:
each class also has 20 sets of tier 4 armor apparently, which means there's 400 sets of Tier 4 armor in the game.
edit:
also mark no it isn't RPS bullshit. Pretty much every class has the same options, just the options are a little bit different in power. It's not like WoW where ONLY ONE CLASS CAN STEALTH IF YOU DONT HAVE A DESTEALTHER YOU BUMMED, or ONLY X HAS Y SO IF THEY DONT HAVE X I AM STRONGER BY A TON (Cloak of Shadowsss).
every class can remove debuffs, heal in some way, buff teammates, shatter enchantments, remove curses, deal damage, etc. Some are just better at some of those than others, but never to the point where its like, WELP WE DONT HAVE X CLASS ON OUR SIDE WE'RE DOOMED.