Nintendo is more commomly emulated, or there consoles are because they were the leading game makers for a number of years almost everybody loves here games and there's a huge selection.
SONY is not commonly emulated because they started out with the PS0ne, which used discs that can be up to 700mb, so its a hassle, I myself use ePSXe
and play FFVII through my CD-Drive, although it has yet to be perfectly emulated.