I'm thinking of upgrading from my SR-16. As crazy as this may sound, I'm considering a Zoom 123.
What sold me was a song I downloaded from the mp3 clinic by Dabluesman. He used a 123, and to my ears I have never heard a drum machine sound so real. If he hadn't said it was a drum machine, I'm not sure I would have known. To me this is by far the most important criteria.
The problem with the SR-16 is the toms don't sound real at all, and neither does the crash, so your kind of stuck with snare, hi hat, kick, and ride.
What's weird is this is the only Zoom product that I would even consider.