Hmm, I agree. I was trying to stay as close as possible to the in-game's description in the opening list, but I guess we can always improve. It's kinda obvious the translators could only squeeze so much info in the game, due to space constraints (compared to how little space kanji took, in comparison).

So what are the most powerful/useful? On a physically powerful standpoint, I really liked Crodechild/Fredegund "Divine Edge" unite. It's incredibly powerful, and allows you to conserve MP for when you wanna use their True Falcon skills on bosses/hard enemies.

Tsaubern and Chein: "Lightning Lash" looks freaking awesome. I love how they just walk slowly towards the enemy and in a flash of ridiculous Dragonball-esque speed, the enemy gets torn up. Too bad Tsaubern isn't as useful as Chein.

it will be nice to group the support character unites separately... so we would have categories for 1 + support, 2 + support, etc

Mascots (Autar and Numnu) damage 1 enemy and seems to do something big like 2x or 3x damage. Also, it can cause Fury to the enemy.
I just tested vs enemies strong vs pierce and weak vs slash and gave both of them pierce weapons since I couldn't give both slash or both strike due to their equipment limitations. For normal attacks, Autar w/197 atk did 311 dmg, and Numnu w/241 atk did 424 dmg. Their unite is ranging from 2800-3000+. I assume their particular unite is elementless since they're just sitting there throwing hearts... I am assuming being strong vs an attack element reduces damage by 30%. If so, their normal damage (if they both could use strike) would be around 1000...
However, now I'm fighting the Soul Eater and it seems to be doing 2x damage.

looks like Sisuca + Marica is 1.5x dmg and also seems to ignore attack element.

Selen + Jale looks like 1.2x dmg

Shining Scalp has a chance to cause Bucket to any ally.

Royal Pride: Shams gets Fury, Manaril gets Alert

I believe Chrodechild does unbalance from this unite however one of her early and most useful marks is immunity to that status.

--edit--
After playing this again i did the unite before setting any marks and she didn't unbalance.