Is it cleverer or more clever?

Cleverer is an adaptation of clever.

As in, Marsha is cleverer than Mark, but Madison is the cleverest of all.

It does sound better to use, Marsha is more clever than Mark, but Madison is the most clever of all.

Fowler's "Modern English Usage" includes clever in the list of adjectives regularly taking -er and -est in preference to more and most.