Now are we talking about character movelists/fighting styles/weapon styles or are we talking about character designs/aesthetics? Cause as far as the new characters the only characters I liked and would like to see return due to their design are Omega and Viola. Zwei looks like a zombie version of a FF character so fuck him (FF DOES NOT BELONG IN CALIBUR!) Pyrrha and Natsu look like a pedo's dream ( I hate myself for thinking Natsu is kinda sexy though) aPat is terrible all the way around and Pat is even worse, looking like an albino human peacock. Leixia is cute but annoying (sidenote-I remember something about when the characters were revealed that there was talk about Leixia looking the way she does to pay homage to Kayane)so you might as well bring back X. Xiba is stupid looking and his move set is just goofy. And since Algol was brought up I hate everything about him. His look, his fighting style, his "weapons", just everything.
Fighting style/weapon styles you can lose all of them. Although Pyrrha is a more athletic version of Sophie there's no need to keep her, Natsu or Taki they're both just jumpy ninja bitches so you might as well just bring back the OG. I always thought an umbrella was a stupid weapon so I'd keep aPat if he didn't look so damn stupid. Leixia is definitely a poor man's Xianghua so get rid of her. Zwei is pure gutter trash, his style was unique but ultimately it proved itself to be a gimmick so trash it. Omega might as well bring back Cass and fuck Viola's moves.
So to sum it all up I'd bring back Omega and Viola if they had different weapons/fighting styles.
I'd bring back Sophie over Pyrrha but include some of the more athletic moves into Sophie's movelist.
X is just a better character overall than her daughter.
I'd get rid of Xiba in a heartbeat now that Kilik is back.
I'd bring back aPat OR Sets if they changed how aPat looked or if they gave Sets something other than a dumbass umbrella to send you sprawling 10 feet in the air.
I wouldn't mind Natsu back with a different move set but barring that if it's a choice I'd just bring back Taki.
I'd just trash Pat. His move set was just stupid. You could integrate some of his better moves with Cass' attacks and bring her back while getting rid of him.
Fuck Algol. I swear he was the souring point storywise for this franchise. His weapons/attacks just compounded how dumb of a character he is and he took the story in a stupid ass direction.
And because I'm old school at heart, bring back Zas, Talim (that hurts me so much to say for so many reasons) and Hwang. Also FUCK MAXI bring back Li Long with his double chucks!!!
FINALLY, I REALLY wouldn't mind seeing some of those SC3 bonus character move sets make it back into the game. Of course they need to be fleshed out a bit more but man most of them brought a lot of variety and were fun to watch.