I'm pretty sure this has been discussed before but....
What is your favorite game mechanic? Cards, Dice, or Bidding? Do you like roll under or roll over, or something else completely? Is there a particular range of numbers that you believe is optimal?
I love a lot of different dice mechanics, but if I had to choose, I would choose a simple 2d6+modifiers, roll over the difficulty number. I think it's clean and efficient. I also like dice pool and dice ranking mechanics (such as featured in the Storyteller system and in EarthDawn, respectively). However, I am always interested in learning about new mechanics... I heard about one that uses a dice pool and measures success by how many dice rolled the same number and how high that number is. Very interesting stuff...