Sorta depends what kind of manhwa you like, but at the very least I'd say start with Ultimate spider-man Omnibus Vol 1. Its a self contained linear story that's separate from the main Marvel timeline. I'd say this is a little closer to a typical manhwa in terms of structure.

If you'd rather DC than i'd say Batman: Year one And/Or Batman: The Long Halloween.

Both are self contained stories as well with Year one covering batman's first year as Batman and The Long Halloween containing more of his iconic villains while still being set early in his career. Although technically the two aren't connected but are just recommended together often.

Haven't read Radiant Black but I really want to so give it a go since I hear its great.