I like players with a sense of humor who are pretty laid back but not afraid to engage the story and the combat. People who don't take the game personally but still work the story. I also tend to gravitate towards games where we're all good and neutral type characters. I love being a player or a DM, so either is good with me.
I've played 3.5 and having been reading up on 4.0. I'm currently designing a campaign for either one. I played a weekly game in a couple of home designed worlds, so I have no familiarity with any specific details of the official worlds.