I handled an SR9 at my local gun shop this weekend, and I really liked it. The biggest complaint I have heard has been about the safety, and sure enough, it wasn't great. Easy to take off, a little awkward to put back on. The guy behind the counter told me that they have sold a few, none have come back, and the customers seem really happy with them. I happen to trust the guy behind the counter, so it wasn't just empty sales talk. With that being said, the MP seemed to have better ergonomics. It wasn't that the SR9 felt bad (it didn't) or was uncomfortable somehow (it wasn't) so much as it was a case that the MP was just a little nice overall, something I attribute to the slightly wider grip. I plan on buying one of the two, and I am leaning towards the SR9 simply because I am a Ruger fan and feel I can trust what they make. Add to that a traditional dislike for Smith autos, and you can see my bias. I would also add that the SR9 is cheaper by quite a bit, although the current deal is pretty good.
I would add that I have shot neither, which is why Glock is still in the running.