I will have to say, PS3/PSP for all PS1 games
XBLA (and some PSN) for all remakes that have upgraded graphics
Wii VC .... I am not that fond of as the prices are outrageous in my opinion. There is NO improvement (they are straight ROMs) and you need yet ANOTHER controller to play them.
However, some of these games are only available on Wii VC so .. its up to you.