US really doesn't want visitors....starts with the long queue and hostile officials at their Embassy....just to get a Visa.....then you face Dept. of Homeland security when you get there.......
Spain is desparate for foreign visitors, is geared up for them, prices are rock-bottom..climate is good........
ATM, I can't think of a single reason to favour America over Spain (never been to either, but trying to walk in the O.P's shoes.)