I have played them both and can speak authoritatively on the matter. They're both shit. For city-based games they have barely any content, and are mostly just comic book combat. They've got about 5 characters and stupid half-assed narrative. They're linear games that happen to have open maps. No radio stations or any creative detail makes their cities dull to explore. Infamous has a better city (barely), but prototype has more creative and complex combat mechanics. Infamous lightning combat was shockingly poor. Prototype had more original ideas but the graphics and lack of variety (just kill things and blow up buildings) let it down a lot. Infamous didn't have destructible buildings though, instead it had dumbed down platforming that a 2 year old could do.