In advance: Sorry for making this post too long.
I'm going to act cool and answe the question in regard to each team (I don't have F5 variants ;():
Prime Wardens:
Favorite 2: PW Tempest, followed by PW Fanatic
Least Fav. 2: PW Captain Cosmic ,then PW Haka (Nothing wrong, I just like the others better)
Most Improved: PW Captain Cosmic. He doesn't spam constructs, but he gets a bit more out of them so they arent just lowest target fodder.
Most Negatively Changed: PW Tempest. Instead of getting the AoD damage Vengeance-style villains despise, you can play extra cards, but at a considerable cost. This doesn't do much if Tempest has a bum hand,
Craziest Change: PW Fanatic. This is a very fun way to play her, and whatever she plays can completely mess you up, especially if you pull an EoD.
Dark Watch:
Favorite 2: DW Fixer, then DW Expatriette
Least Fav. 2: DW Nightmist (never understood her), DW Setback
Most Improved: DW Fixer. Hate the price, love the item. None of the three I remotely can play well are better, but this is the least saddening to play.
Most Negatively Changed: DW Setback. Idk if it's just me, but I need tokens to play well.
Craziest Change: DW Fixer. He has to destroy the things that were once important to him, but in severing that connection, he is more powerful than he was before. Vanilla Fixer was better, but this man uses Bloody Knuckles better than anything I've seen before.
Freedom Six:
Favorite 2: EoW Bunker, and afterwards is Price of Freedom Wraith (Not nesc. the power, but the story...)
Least Fav. 2: Sac Tempest, and Golem Unity (Don't hurt her!)
Most Improved: TLT. Nothing to say, other than the woman is a cheat code.
Most Negatively Changed: Sac Tempest. The draw is nice, but I already have a card that lets me do that without giving up my babies.
Craziest Change: AZ. Who knew you didn't have to do a lot of math (at least, in the beginning) to get this guy right?
Termi-Nation:
Favorite 2: Bunker and Unity
Least Fav. 2: AZ and Unity
Most Improved: Bunker. (He-man voice) I HAVE THE POWER!!!
Most Negatively Changed: AZ. I can't work with him like this. Maybe someone smarter, but I just can't.
Craziest Change: Unity. Flips the script on golems.
Finally, i have a parody to the first verse of Bad Day by Daniel Powter about a variant that I'm always sad to play. See if you can guess.
Where is the damage we needed the most/You kick up the myths and the magic is lost.
And maybe you're sunfire's gone, they say /They tell me your fun has gone away
It's much too hard to carry on...