You should build different teams for different situations.
Normal Story Mode
For normal story mode on easy and medium you should have one of every type on your team so you can deal with most situations. Basically add in characters that link together or are your strongest units. If your lucky enough to get a Frieza or SSR unit build a team around him that works in favor of their Leader Ability and Link Skills
Tough Boss Battles
For boss battles that you can’t beat, event bosses, and z-hard stages on story mode your goal is to build a team that is full of the Type that goes against that bosses type. e.g. if the Boss is INT (purple) have PHY (orange) types in your team, re-arrange your attacking units to have the boss hit your strongest PHY unit every time. This will more than half the bosses attack. Don’t have any units that are going to be weak against their type (the color to opponents color is pointing to) so if the boss is Purple don’t have Green units on your team because they will do very little against your opponent and get attacked for huge damage.