I use Cubase at home, and Reason at school. So far, I like Cubase for its amazingly flexible routing and setup. I use Battery 2 for my drums, and I can send each drum through its own output channel and EQ, compress, add effects etc separately, TO EACH DRUM! I love that. Yes, you can do lots of those things inside the VSTi too, but I like having them there right alongside my regular audio tracks, doing the same kinds of processing to them.
That said, you can get a heck of a lot of action out of Reason for the money. I just started using it this semester, and don't know all about it (don't really care to since I'm not planning on buying it) But it seems very complete, yet geared toward electronic or other non-organic sounding music... stuff where a drum machine sounding like a drum machine is a good thing. I could be wrong about that, but that seems to be the case with a lot of the instruments.
To me, I would always choose a computer setup over a stand alone synth for what you want to do. If you were a keys player looking for a gig-rig, or a nice keys module for your studio, I would recommend the mo6, but for serious rock and roll production, you'll be better off with some good VSTi stuff. Besides... if you don't like the reverbs etc in the mo6, whatcha gonna do then?? If you have Cubase, you can just try a different effect.
As always, YMMV.
Peace!
~Shawn