I prefer games with mechanics that differ from each other. Games to similar to 3.x can confuse me because it can be hard to pin down the differences between them and 3.x. Retro clones don't interest me because I'd rather just play the original game.New Question: Do you like/prefer games with similar core mechanics?
I like roll low systems because they're easy to grasp quickly. One of the reasons I like Rogue Trader and Deathwatch is that they were quick for me to catch on to the basic system.
Dice pool systems seem to take the longest for me to master, but lots of games I like use them. Changeling: The Dreaming (2nd Ed), and Shadowrun 4e use them to great effect.