Well, first there are two types of players, the ones who recognize girls and team strategy and the ones who don't.

The latter just look at TP/Speed/Attack type. Since this is the forum, I'm guessing you're not too worried about them

For the former, I'd say you have four options:
1) Power focus: Rainbow heavy, with lots of attack up and possibly enemy damage down
2) Speed focus: this is event-specific, since some events like high speed, others really low. Only a handful of story maps want lopsided speeds
3) Self-Sustaining: Heal/Attack Up on Pest Node, -50% damage from pests, and a girl or two with self-healing skills. Should be fast since you want those Heal/Attack buff on pest nodes to be running ahead of other squads so they actually have pest nodes to run over (Alpinia is ideal since she has Team Speed +150 AND Self heal skill, plus rainbow stats)
4) Some combination of the above.

Jack of all trades squads are feasible but without 5 rainbows in one team (or at least 4), it can turn out poorly (think about Defense buffing in particular with some girls and their low defense, high HP stats, as an example). Synergy is better. The squad Balkri posted is a mix of options 1 (power from Cactace) and 3 (the rest are a great sustain combo; Orchid has a self-heal skill in addition to her speed boost, she's basically a 5* version of Alpinia)

At present, there's no real reason to obsess over having all 4 attack types in the group. Ability synergy, speed and sustainability are much more important, along with raw power if you've got 4-5 rainbows to come out and play