I prefer both, but usually PvE is the best because it's tends to be the most balanced in an MMORPG, though some games are great at also balancing classes for PvP as well.
Both, it depends on what mood I'm in. Usually when I'm fighting mobs it's to get a drop or quest completed, if I'm PvP'ing then I'm just looking for a challenge.
PvE. Most of the games i played like MU had pvp systems that made new players be in great disadvantage as most of the times better gear was more important than skill, so i always tried to avoid pvp as losing all the time is not fun at all.
I love both. PVE helps level your character. How can you PVP if you're level is too low to hurt a fly.
