Ho boy there's a lot. Just with the base game, Bunker and Absolute Zero are some of the most complex characters to play as, with Zero in particular being able to do all sorts of crazy fire and cold attacks once his setup is done. I'd put Visionary up here too; she plays a completely different game from the other heroes. She's very good at manipulating various decks and giving interesting effects to heroes (such as Twist The Ether, applied on a target which can change their attack type and can also increase or decrease that damage).
From expansions, Mister Fixer is more varied than Expatriette as he has tools and styles which he can switch on the fly for many situations. He can seem a bit weak but the rewrite on his Dual Crowbars can greatly help out his damage potential. There's also Argent Adept, who uses instruments and aspects of music to call forth different kinds of effects, including throwing out additional powers and plays to other characters. Nightmist also has a spell system where the effects of some of her attacks depend on the number that is specified on that card or cards on top of her deck. Then there is Omnitron-X who, if you've fought Omnitron before, you know what his 10th iteration is like. Between playing components, platings, and throwing timeshifts around, Omni-X can be a tank, a damage dealer, a healer, and a deck manipulator all at once, so long as you don't get his components destroyed by receiving 5 damage in 1 turn.
As for Guise, he's a crazy silly character who is all about three things: Playing cards out of turn, drawing cards like crazy, and using the abilities of other heroes in play to his advantage. He takes a couple rounds of setup, but he's capable of doing hilarious things in a round once he's got enough ongoings out and has the right ongoings and equipment "borrowed" (incidentally Fixer is one of the best to have for Guise, as Fixer's styles and tools happen whenever he does damage, and Guise can basically hit once or twice every turn).
I also found out Guise is also a massive counter for any villain who tries counterattacking whenever you deal damage them. I'm not being hyperbolic when I say Guise by himself literally makes Advanced Chairman kill himself in a single round. :smallbiggrin: