Lets break it down....
PvP, Bread and butter! If you want to beat the crap out of a human rather then a line of code this is what you love, all about having the bigger better connection PC and settings, you got your cheaters(hackers), people with no moral values, and those who only care about pushing that extra kill!
PvE, Raids content, everything core of any group adventure, not competitive. Nice to build your character with but lets be honest we want beat players.
RvR PvP on a larger scan? Say no more...that it for some reason always fails.
GvG This is my bread and butter, taking pride in your group and putting others down. Various forms of this have popped up, WoE in Ragnarok Online, is where I hardened my PvP and GvG interest, I really look too loved the concept of groups of players rather then factions fighting the the generic good vs evil, or orc vs elf that you see ins o many fantasy games that have PvP.