Which macbook pro should I get?

(No apple hate please, im getting a macbook. period) I need a system that is capable of running World of warcraft and starcraft 2 at low graphics (maybe medium? if not, np) with decent framerate. The two im choosing between are the 13 and 15 inch both with i7. which should i go with? the 15 inch is 400 bucks more $$$.