SNES version will probably run better, but the PSX version has an increase in difficulty along with characters having abilities that werent allowed in the SNES version (Cecil's "Dark Wave", Rosa's "Prayer", etc). Also, I think there are FMV cutscenes in the PSX version as well?

Both copies are expensive I bet (probably less so with the playstation port), but I'd try to get either one. If you can't find them for cheap, there's always the GBA version! (my favorite version lol)