Over the last year I've invested considerable time giving SO3 Pro and Reaper attention.
Initially, SO3 was very quick to get going with and has a great set of features. At this point though, Reaper is my favorite. I had to find a theme, menu replacement and create my own toolbars to make it usable for me, but the good news is that those things can be done.
I'll prolly keep SO3 up to date for a while to see how it shapes up, but for now it will be Reaper for me.
Yes, SONAR will likely continue to work for a good long while, but I can't see getting behind with what I'll eventually have to move to anyway.