1155 is better, its also quite a few years newer. if you buy a 775, it will only do 775 supported processors (core 2 duo, core 2 quad, etc). if you want to use the more recent (second and third genereation) i3/i5/i7 you will need an 1155, if for some reason you want a first generation i3/i5/i7, you will need an 1156 motherboard