After Effects is much better IMO. Motion has no soul, but if you're looking for easy, slap on, pre-made effects, etc., get Motion. But if you're looking for a real program that you can create signature effects with, go for After Effects.
p.s. I personally think that keyframing in Motion sucks compared to AE too.
You can't even compare the two... Motion is a toy. If you want to do something serious go After effect, I would also take a look at combustion which I actually prefer over After fx.