Out of those three choices, Zidane and Garnet hands down. The other two pairs don't even come close. Tidus and Yuna were somewhat believable, but Squall and Rinoa were about as fake as you can get. The best romance in any Final Fantasy is probably between Cloud and Aeris, or Locke and Celes. Delita and Ovelia was a great pairing, too, but they (unfortunatly) never really got any recognition.