Depends on the game. I own all the originals and then some of the remakes as well.

I - NES, PS, GB
II - PS, GB
III - Just a rom. I hate the 3d remakes.
IV - SNES, PS, GB
V - PS
VI - SNES, PS, GB
VII - the rest on PS. I think I might still own a PC copy of FFVII somewhere too.