Dr. Doom is my favorite villain. I love that he uses both science and sorcery and that he's incredibly smart.
The Flash is my favorite hero. He's rather OP, but I really like how powerful he is compared to other traditionally powerful characters (e.g. he took Wonder Woman out using an infinite mass punch).
I also really liked Doc Oc as Spider-Man. I wish they'd have just left it that way.
If I had to pick one Swamp Thing. good horror/suspense, lots of places to go with the art and story, & bumps into some of the weirder cast of DC characters too.
Marvel: Too many to name, but let's go with an oblique character — I read a lot of X-men before Bishop came on the scene. He was the first new black man to enter the fray in a long time in my reading of comic books. I'd never really liked Power Man/Luke Cage, nor did I have much contact with T'Challa / Black Panther or Rhodey/War Machine. Also, Nick Fury wasn't black yet. Wolverine is Canadian, but not black, and Storm is black, but grafted onto the same default "comic book beautiful woman" frame that almost all others were. So, Bishop made an impact on me at 14 that few other character introductions could. He was my example for the importance of representation. I actually looked forward to Hallowe'en that year.
DC: I never liked DC. Too saccharine. Too Star Wars. Not enough moral gray. To that end, my fave DC character is Amanda Waller. Uncompromising, unrepentant, and driven. Don't fuck with Amanda Waller. She would find a way to bury Batman.
On average, Daredevil is my favorite comic character, period. Not necessarily every single story arc, or every writer's take, but the overall character that is beneath all of those.
My favorite DC character is usually Batman, but they reboot so damn often that it makes it hard to have a relatively stable character at all, so it's more that I like the idea of Batman, and enjoy only some of the story arcs here and there.
Daredevil at least has a relatively consistent personality and ethos. Otherwise they'd be equally "favorite" for me. I really dig the idea of what is basically a regular person that has no or no extreme powers doing their best to overcome tragedy. Yeah, technically, DD has a super power, but it isn't very super, it comes with limitations and one of those limits is that it's only perceptions. That's really no different in scale from Batman's "genius" imo.
Mind you, with all of that, my "favorites" are really thin margins between them and the rest of my "favorites list" that are below them. And there are eras of a given character or a specific story arc where a character that would rank lower as a character ends up being much higher. An example of that is The Immortal Hulk storyline. Probably my second or third favorite story arc ever, despite Hulk being further down my list than someone like Spiderman, that I really like a lot more as a character overall.
Daredevil is my favorite. Most of the iconic writers we know today like Miller, Waid, Brubaker, Bendis, and Zdarsky had their fun with the character on their own runs and it definitely shows.
On the DC side it's hard to beat James Robinson's Starman. The SW6 Batch of Legion of Super-Heroes was quite good too.
On the Marvel side I kind of have a love/hate relationship with the X-Men. I love the characters, and some of the stories, but when it goes bad it goes REALLY REALLY bad.
The Age of Krakoa stuff started off great, but then literally dove off the deep end with Moira's heel turn.
I know they're going to resolve it all soon and bring it all back to the mansion and frankly that can't happen soon enough.