I like to use all party members equally, but in the Final Battle I used Zidane, Freya, Steiner, and Garnet. Zidane of course is mandatory, Freya has one of the best abilities in the game, Dragon Crest (just a minute, I'll explain why), Steiner is a great warrior and has the best Trance, and Garnet rounded out the party as the healer -- I picked her over Eiko for her Curaga spell (which I believe Eiko cannot get . . or it's more difficult to learn with her).

If you're starting a new game, use this great trick I learned to level up midway through the game: Steal a Coral Ring from Beatrix (the 1st battle with her, I believe), or buy/synthesize one. Also, have Quina learn Level 5 Death. When you have both of these, put Quina (equipped with the Ring) and two of the above people in your party, and go to Gizamulke's Grotto and up the vine in the back. You will be on a section of the world map, where as long as you stay out of the forest, all you will encounter is level 60 Grand Dragons. The only seriously dangerous attack they have is lightning based, which Quina will absorb . . . just have it use Level 5 death on the dragon, and it will go down in 5 seconds. That's almost 2 levels per fight, depending on how early in the game you do this. And, killing all those dragons will power up your Dragon Crest ability, making it an easy way to deal 9999 damage at the end of the game (kill 100 dragons and you're set).