While some people seem to like mono or dual colored teams, I normally play with an even spread of colors.
I normally care only about ATK and not so much about HP, Heal or powers (unless for special levels, like some Expert levels). Therefore I put all available stat points for all characters into ATK. I will also assume that for each character the maximum number of additional stat points is added via fragments and spent on ATK.
This adds an additional 570 ATK to the base stats of each character. It shouldn't have that much impact to which team will be the best (since the additional ATK is distributed pretty evenly among all colors), but since I'm presenting fun numbers, I want to go for the biggest. ;-)
For others who feel the same, I present here the team with the highest minimum damage across all colors (tiebreaker being the highest second lowest attack etc.):