The game: Final Fantasy V
The contenders: SNES, PS1, GBA
The winner: GBA
It's really no contest. The SNES original is only playable in English by a fan-translation that was utilitarian if nothing else. It's scarcely better looking than Final Fantasy IV. The PS1 version is slow, glitchy, and has a worse translation than the fan translation.
The GBA remake is pure awesome. Excellent translation, excellent artwork, and modernized to fit in with modern Final Fantasy games (-a, -ara, -aga instead of -1, -2, -3, 'Holy' instead of 'Pearl', etc). Plus it has post-game content!