Depends on my mood, I buy blocks/wedges of either depending on how I want my homemade pizza to taste, or what kind of pasta i'm making....but if I really had to choose I'd say Parmesan because of the nutty earthy flavor that I really like. Pecorino Romano can just honestly be too mild for me.
Generally for homemade pizza I'll use fresh mozzarella(you know the stuff that comes in a brine)
I'll freshly grate some Parmesan Reggiano and just a touch of a local hickory smoked provolone cheese freshly grated of course.
Plus fresh basil, a touch of olive oil, and julienned shallots, simply outstanding pizza.