Mad Jack (Jack O'Lantern) I'm a sucker for Halloween gimmick baddies.
I also really like the Alan Fagan version of Mr. Fear, but he is probably considered more C-list. (Not many appearances since "Web of Spider-Man", and when he does it's usually as a background cameo villain, or that tiny role in "Breakout" mini.)
I'd say the Jason Macendale and Phil Urich versions were solid b-listers at best.