I've seen about the same number of movies featuring Perkins and Combs, maybe even one or two more from Perkins. As much as I enjoy both actors, even when the movies they're in aren't so good, I have to go with Perkins. I'm a massive fan of Perkins in the original four Psycho movies.
In my experience Combs has the best performance and film, with Castle Freak, but I'm not sure I've ever seen him play, nor think he could play, an entirely normal, likeable hero figure as Perkins could (The Tin Star comes to mind). I might give an edge to Combs just because I'm a mad scientist fan. Perkins is wonderful as Norman Bates of course, but I'm not sure he stands out to me as much as Combs as Herbert West or Dr Crawford Tillinghast