Well, my "favorite" party would Be Amarant, Eiko, Quina, and Zidane (ehhhh, shaky on that. but I love the first 3)

However, I've found that the strongest in terms of battle and tactics is the all-female/??? lineup. Eiko, Garnet, Freya, and Quina. This party is pretty much an unstoppable juggernot just waiting to be released. Eiko is by far the better summoner/White Mage, but having another, even if it is Garnet, helps. Quina only needs, Frog Drop, White Wind, Magic Hammer, Angel Snack, and Auto-LIfe to be pretty unstoppable by him/herself. Freya always does 9,999 with Dragon's Crest. Quina does 9,999 with Frog Drop, Garnet does with Atomos, or Bahamut if I'm in a boss battle, and Eiko is there for Carbuncle, Madeen, Phoenix... in that order.. over and over... endless, unbreakable cycle that kicks your patooty.