I know a reason why many end users prefer other emulators over MESS,and mind you these are just end uses.MESS has no cheat support.Or should I say no easy way to cheat in games like other emus or even MAME.No end user wants to open a debugger and make their own cheats,before playing a game.they want to open game,open cheats,select cheats and play.
Ive setup quite a few gaming setups for people I know and they all want to cheat in old games.Mostly because they just dont have the time to play them fairly,(or more likely the patience\skill) and they all want to see those later levels they could never get to as a kid.