Comment by llllllllllll

It's good practice to check your intuition on things like this against a searchable corpus. According to http://corpus.byu.edu/coca/, "most wicked" just barely edges out "wickedest" in terms of frequency, 22 to 20.

An example that strongly goes against the rule:

simpler (3185) / more simple (153)

simplest (2191) / most simple (87)