Anything productive. Not a fan of just sitting around doing nothing beneficial. Leveling, making money, scoping the FM rooms, etc
Well personally I enjoy PQ the most. Its just much more fun than doing things alone. PQ's always involve other players with me. Being a loner in an online game is quite difficult unless you're really persistent about it. I learned that the hard way.
I cant choose just one option, so I didn't vote. I like to stalk people and hang out with them. I love quests, PQs, and I like some bossing but I like challenges more so than the run of the mill zakum run. I like events and participating in them. I like to help people out, farming stuff for people just to give it away, etc. (like skillbooks from monsters instead of bosses)
Discussing end tier content with guild members, research on some guides and grind on my Bishop all day.