RM2 / C is a bit quicker for character creation. This is mainly because it gives each skill an independant cost instead of using costs assigned by skill category. It also assigns stats to skills individually instead of by category. It doesn't have different skill progression rates, for example Body Development (hit points) provides a die type by race size instead of a fixed progression by race size. RM2 also has a different turn sequence, though I'm not sure it's possible to say one is better or the other worse, they're just different.
What you sacrifice is the capacity to broaden the skill list without adding another great big chart and a much more complete and better supported game. You also move into the land where every group's RM2 looks very different because of the house rules and options being used.
RMSS offers many very nice features, such as talents and flaws, training packages, and culture packages that aren't implemented in RM2. The differences in Arms Law and Spell Law between the editions are really pretty small.
