I had the same question. I found this site.
Motif VS any Synth.
http://motifhelp.tripod.com/motifvs.html
It seems if you want strings the triton is the way to go.
If you're looking for keyboards, Organs, Pads, drums go Motif.
Me personally, for hip hop I use my Mo phatt more than my TritonRack.
The presets were made for hiphop. And once you learn to program it you can get the sounds you want. It has a growl to it for the sreet the triton doesnt have. To me the triton sounds are to clean. Rap to me was not made for orchestra strings. THe guitars and drums in the Mo Phatt destroy
the triton. It's not even close.