I enjoy Armor quite a bit. She's not as cheap as Jubilee, but she's a solid enough Mutant Sidekick for an easy to add on price. If you're not running builds with Professor X, Cyclops II, Chuckernaut and the like but still want to go heavy on Mutants, Sidekicks are where it's at.
She only gets you an extra attack of 4, but she's fairly sturdy. 3/B
Bishop has gotten a little better as the Lawman faction has expanded. His main issue is that his ability set is sort of dependent on opponents agreeing to power you up when their best move is to just close in and attack adjacent. Not sure there are terribly many good strategies to get around this. 2/C-
Cable is all about getting him on height with attack boosters and using his double attack and sighting. The first ability might as well be flavor text. With Punisher's multiple normal attack going the way of the Dodo, Cable took the crown of "attack booster's best friend." 4/A
Phoenix isn't necessarily as scary as some of her later forms, but the Phoenix stack is an effective way to play her and she's also a Unique Hero Mutant Telepath, so she has all sorts of synergies to build around, even if it's just using her in a Prof X army. She's a reasonably priced and fairly efficient auto wounder and figure mover, which are pretty useful abilities in the meta. 4/A-
Forge is a bit of a mess. His first ability requires either another good glyph around for him to copy or Mutants around to negate. In the right match up, I guess he could be really devastating, but in that unfun to play against way. I'm sure there are good glyph copying exploits with him, but none that are really defining the meta. His other ability is dependent on you bringing along species that don't mesh with a desire to run him in Mutant armies. I guess he can heal himself at least, but at 4 Life, 6 Defense, and no defensive ability, he's just as likely to fall from one or two turns of focusing on him.
I went with a slightly OK score (C+ above average) just because of potential glyph shenanigans. But I think he takes a lot to squeeze competitive play out of and for me the juice isn't worth the squeeze.
2/C+