What Marvel/DC character, character group, or anything else do you think would be best suited for an anime adaptation, and why? I'd say Spider-Man because his charisma, multitude of suits, other Spider-characters, multiple different interesting story-lines, and other stuff adapted in an anime art style, and tweaked to fit as an "anime" better would be intriguing as hell to see.
I'm gonna be honest right now, marvel and dc would suck as anime. They already tried to make a few of them and they all sucked.
Examples:
Batman Ninja
Avengers Confidential Black Widow Punisher
Well, since "anime art style" can mean a plethora of things and even look like american comic books, I'd say it all depends on how far do you want for the show to cater to Japanese people. Deadpool is going to be an easy choice, because his manga is currently selling really good in Japan.
Marvel side I think Big Hero 6 might work out. After all it is originally a japanese team. Then there's also Power Pack which can be made as a show for kids, as it follows 4 siblings who are colored in Super-Sentai manner and have very “villain of the week” like adventures.
Peni Parker, possibly. Her original version in the comic books is far more enjoyable and is probably adaptable to Japanese market, than the one appearing in "Into the Spider-Verse" cartoon. She's badass and is basically Rei from NGE. Exploring her universe would be a great thing. Although they would have to cut out all Akira/GITS/Trigger/Gainax etc. references.
DC wise you could probably make some Tangent-like universe, where all the characters are basically different and adapted to Japanese market, because their original japanese teams are bit too stereotypic and I'm personally fed up with yet another Batman cartoon.
Basically, they have to "Witchblade" it. The original is American comic book, which is adapted in japanese animated show, but they transported the plot into Japan, created new characters and etc.
Ironman but have it look like Cowboy Bebop or something. :P
For real though, superheros are basically magical girls but for a male audience, so just making the comics into animes should work decently enough. Sadly, I'm not too knowledgable with comics but I'd personally like seeing all kind of futuristic gadgets hand drawn and would genuinely like seeing Ironman or Batman. If it however is CG then I'd rather watch a comedy akin to Teen Titans but with a different cast. Kinda like Isekai Quarted but a bit more serious if possible.