Well, since both are implementations of the Modelica standard I would guess they are pretty much the same, though I do not know MapleSim or your problems with it.

It was extremely difficult to model two interacting surfaces -- for example, a wheel rolling on a surface with friction.

Well, not my area, but a little googling brought up this: http://www.inf.ethz.ch/personal/cellier/MS/andres_ms.pdf (well, there goes my evening). I don't know, but I find the decomposition quite intuitive.

MapleSim only implements a subset of the Modelica standard.

if it's like Mathematica vs MATLAB, then it will be much less unpleasant to use. one of the reasons i like Mathematica is the consistent respect for UI/UX