I want to compare MapleSim (Maplesoft) to SimMechanics (Mathworks) what should my criteria of comparison be?
I think the most important criteria are
the purpose of your simulator (do you need contact physics? how complex are your models? )
your fluency in both solutions
the size and quality of the documentation/community
is the code you are going to write for the simulator re-usable for real system ?
what is the licencing policy of the simulator (and its price)
In general there is no magic simulator, each comes with its drawbacks and plus. So the choice of a simulator is a compromise between your needs and the solutions available on the market.