I alternate between two different parties. My first party is Vaan, Ashe, and Fran, and my other is Basch, Balthier, and Penelo. Everyone is always within 2 levels of each other.
Same here, I have two tanks, two healers and two ranged attackers
I also do one team with Magick and one with Techniques on the gambits.
This way I have always people with full MP bar for quickenings