The skill sets are different, but assuming you can attain an equal skill level at each, here are my guesses:

MTTs are profitable for a smaller percentage of players than STTs. For an even smaller percentage of players, then, MTTs are more profitable STTs.

MTTs have much higher variance for playres of any skill level. The difference is probably enough that anyone playing a particular buyin STT because of bankroll rather than skill would be better off playing STTs than lower buyin MTTs.