Sorry, I'm a bit late to the party, but I felt like adding my 2 cents.
I have both synths as well. I must say that as a learning instrument, the sh-201 definitely comes out on top. It certainly helped me understand subtractive synthesis in a simple logical way because of how it is all laid out.
The sh-201 also works quite well performance wise, once again because most parameters are tweakable right in front of you, plus the d-beam is fun, and quite configurable.
*also* the sh-201's vst plugin interface is awesome if you have it connected to your pc alot, you can save patches and tweaks in your software of choice. which is much better than the pc editor that comes with the r3, even though the r3 editor has a nice midi monitor that comes with it.
where the r3 wins out is in it's sound engine. the r3 just sounds better, plus you have more to work with, there are three effects layers you can run your sounds through, and there are quite a few awesome effects you can use. The distortions and amp modelling on the r3 are awesome, much better than the very limited overdrive on the sh-201, which sounds pretty average.
The vocoder on the r3 is great. the little lcd displays with the customisable knobs on the r3 are also good. i like the that r3 is portable, i've picked it up with one hand during performances and played it with the other. the r3 has virtual patching, which is a bit limited but certainly way more powerful than the limited options you get with the 201's lfos. also the r3's arpegiator and programmable modulator are way better.
also when you save patches with the r3, it remembers the octave you are in.. one of my pet hates is that when switching patches on the 201, i also have to make sure i'm in the right octave before a song starts.
also the r3 is alot smoother with pitch bending, you can easily hear the 201 'stepping' up when using the d-beam or the pitchbend or portamento, where i don't really notice any stepping with the r3.
however, while the r3 sounds lusher, the sounds on the 201 are nothing to sneeze at. the supersaw or whatever it's called, sounds nice and fat, and it's really easy to program up some nice lush pads or thick leads. The pulse wave is really easy to set up with some nice modulation for those old-school sweeping basslines, and the feedback osc is pretty cool.
overall though, i think they both cover different areas. the r3 has more features, but it's smaller, larger to program. the sh-201 is better play around with, tweak, and it's great for performance, and it's easy to save in a computer software workflow. If i have a sound in mind, i can usually dial it all in with a few minutes of tweaking, where the r3 would take ages of going through menus and the like.
I would say, get the 201 if you are new to synths, and want something that will let you grow and learn without much study on your part. I don't think I could have had a better introduction. Having said that, I'm planning on eventually swapping out my 201 for a prophet 08, or something similar, but i have the feeling i'll always have a place for my r3, if just for a nice portable keyboard/vocoder.
wow, that was alot longer than I expected, I hope it helps someone decide, as these are both great entry level synths.