I'd say start with IX actually. It's traditional, it's fairly straight forward (no fiddling around with materia or junctions) and it's very good.
I always recommend people start with VII (it's where I begun), but graphically the game has aged a lot worse than VIII or IX, or indeed any of the SNES-era games. If you can put up with the graphics though, it's a very good game and well worth your time.
VIII is my favourite Final Fantasy game of all time though, I'm just not sure it's the best place to begin.