My preference is Blitz.
You might get a blitz situation in real games, but almost never a bullet situation, in a complex middle game, mostly an endgame. Why simple spend time playing an entire game in 1 minute, when you might need to use it only for 1/3 of the game(endgame). On the other hand, blitz will actually help you, because there can be middlegame situations in which both players have less time.
Playing Blitz too much blitz will make you play fast though, which will be a disaster for tournaments with the standard time control(90|30), so bullet will definitely be much worse.
blitz