I'm kind of like Chaosmancer in that I love basically everybody, but to touch on some of my own favorites:
So like I said I like Argent Adept because I'm a big fan of both playing and listening to music and thus of playing D&D bards, so a bard superhero is like basically the best thing ever. His deck is also an incredibly versatile and strategic support deck, which plays into my typical gaming style quite well. Also the fact that he's cute and I have a fondness for redheaded fellas doesn't hurt any either.
I also have a soft spot for kid superheroes who are enthusiastic about superheroing and think it's fun and exciting, and Unity, Idealist, and Thiago!Ra all fall adorably into that archetype. Also Unity and Idealist get to make robots with their minds (albeit in different ways) and Unity's deck involves fighting with a robot army, which is the best thing ever. Especially since "robot minion army" is often a villainous trait so it's nice to see a heroic take on it.
While I already liked playing Absolute Zero's deck for its complex & offbeat approaches to combat, I like AZ himself even better after his podcast. I like that he focuses on how music affects culture (though I'm more into folk music on that angle than R&B), and spends time thinking about ethics and humanity in general. Also I can relate in that he's sort of worked through his depression to end up on a sort of anti-nihilistic attitude I tend to share myself (life sucks, people suck, everything sucks, but that just means you should try to do what you can on a personal level to make it suck less).
With Setback I can relate to his bad luck and having everything go wrong all the time (though I admit I am much much much less positive about it), and I mean he's pretty much like a human puppy dog, you can't not like him. Legacy might seem to serve as the SotM world moral center, but I think Setback is probably the one who qualifies as nicest guy on a personal level.
Finally, I can relate to Parse's data analysis skills and social awkwardness, and her deck is pretty much the SotM equivalent to a Blue/White Control Deck in Magic which is my fave style in that game. Also I wish I had Parse's hair.
In pure playstyle I find myself leaning to play the Prime Wardens a lot because they're basically Shenanigans: The Team.
On the villain side, Baron Blade is one of my favorites. I love mad scientists, and he's pretty much the platonic ideal of the aristocratic mad scientist. I so can't wait to see the Luminary deck.
I guess technically Citizen Spring is a villain? But I love her, she's so sweet and adorable and has the world's most tragic backstory. Poor Citizen Spring. :(
I love how creepy and freaky Spite and Biomancer are (also Biomancer is another mad sciency type), which makes me kind of sad that Spite's deck is so not-fun to actually play.
Greazer is downright hilarious. "Rockabilly themed alien bounty hunter" falls under that category of things I never knew I needed until it was presented to me. Also I mean, he's kinda polite for a villain in a way; he pretty much just takes his bounty and leaves, nothing personal to the rest of you.
In terms of playstyle, I like both Akash of the Many Names and La Capitan, since they tend to be fun damage fests but still with lots of strategy involved.