I'd say whichever you feel works for you. I made it through the game just fine by specializing everyone according to their default roles. My main party through most of the game was Fang, Vanille/Lightning and Hope. The only real requirement is to have some form of healing present but since everyone can learn at least some basic healing spells, you could probably even go without a main healer if you really wanted to.

Equipment helps make battles a bit easier but it's by no means essential. I tended to stick with the absolute basics, +HP +STR and +MAG, depending on who I was equipping. If an enemy or boss had an annoying status attack I'd try to get an accessory that reduced or blocked the effects.

As long as you like the characters you're using and you have a decent Paradigm deck, you should be good for most of the game. I can only think of maybe one or two battles where you might find yourself switching out party members, but those exceptions are few and far between.

~DragonHeart~