MACMess is ok if you simply cannot find a quality emulator for obscure systems.
(Such as ASTROCADE)
I have loaded my MACmess with dozens of such systems and the idea is good but
definately could use some tweeking.
As for running STf or STe softwares, I prefer NoSTalgia, the best emulator for MACs.
It is so close to an actual ST, I sometimes find myself reaching behind the keyboard
for the ST's reset button.
STeem not so impressive by comparison but then it is for crappy PC machines, isnt it?
A fixed budget does that to ones ability to choose between a VW or a Ferrari. ;D

Merry Christmas all you Atari fans. :)