Always go bigger.... There is not a darn thing wrong with using bigger wire, and no matter what you do in the future, you will never have to revisit it, get 10/3 + ground cable, you can still use dual 20 amp breakers but will always have the opportunity to swap out the breakers for 30 amp if you want.... Its a minimal added expense now, but piece of mind will last forever.
I originally ran dual 12ga 20 amp circuits and figured that was overkill back when I did it, and just recently added 2 more 30 amp 10ga runs to the system. I know I will never have a need for more power every again...