Originally Posted by Unregistered

It's OK for you to do this with your own squad composition. However, you should remember that most people aren't going to bother with an in-depth analysis of their helper squads. They'll have favorite allies they know they can rely on for certain performance parameters, but if they're looking at new helpers they'll look at total power first (which gives the edge to the tanky girls irrespective of their true strength), then speed and/or special abilities (Edelweiss, Lilac, Chocolate Cosmos, etc.). Some will look for multiple rainbows, which if they're maxed is about the same as total power anyway. None will go to the wiki to research whether a low-power girl's higher attack value will compensate for her lack of HP...they'll just assume that person just doesn't have any higher-power girls and possibly pick another helper.

Basically this. If you don't already know certain girls' images and know those girls have certain useful abilities (Edelweiss, Toad Lily, Chocolate Cosmos even, etc.) then you're going to end up picking based on three factors:
Speed
Total Power
Rainbows

Personally, I don't even care about the stats too much because my own squads are strong enough to clear all current content. So I pick based on Speed alone, really (helps with certain maps to have an extra 650+ speed squad, I have a 630ish and a 700+ but the other two squads are like 470 and 540). However, if I'm running one of the pest-heavy maps like 12-5, I tend to focus on the presence of the Edelweiss/TL combo just because it's useful (even though I once had my Squad 1 reach the boss of 12-5 at about 15% HP each due to small pests and they still killed it without casualties cuz they're all evolved 50+ rainbows it still helps)