From the Game WISH page:

How do you choose games to join or to run? What factors influence you: timing, people, system, genre, etc.? Do you weigh different factors for different kinds of games, e.g., online vs. tabletop vs. LARP? Is it a group decision or a decision you make on your own?

The answer to this question is quite simple.  I play what game that the rest of my gaming group decides to play.  Although I have some say as to what this game might be, my opinion in this matter seems to be a minority share in the decision-making process.

If I were not married to this group I would still probably choose what game to play based more on the players that were playing than the game or game system.  I don't game to game, I game to gather.  Roleplaying would be a pointless frivolity if the people I played with didn't offer some joy in the playing.  Otherwise, I could sit home and waste my time with computer RPGs.

But then, if I broke it down into choosing between games with players that I globally enjoy:

I currently have a finite amount of time in which to game.  Playing on a compatible weeknight might be better for me simply because I wouldn't have to miss any games when I take a weekend away from gaming to visit relatives or play with my kid.

I typically enjoy either heavy roleplaying or heavy die-rolling games (board games like Warhammer Quest or Talisman).  I don't like heavy rules games that pass themselves off as roleplaying.  In that case, like for D&D, the group I play with must be extremely roleplay-competant.  (Unfortunately, I don't have the luxrury of making this choice these days because there is only one group with which I can game.  This is a very hot topic for me nowadays.)

Genre doesn't really bother me at all.  I would like to try some new things.  I would like to try some modern horror that's not White Wolf, particularly something like Atlas' Unknown Armies or Feng Shui, Deadlands (not the d20 version if I could help it) or possibly something like a modern Call of Cthuhlu.

Primarily my group wants to play 3rd Edition.  Because they're all min/maxers.  I hate them.  But they all eat chinese food, own and use computers, and like the same kinds of movies I do (generally speaking), so where else am I going to find such a fine gaming group?