Here's my honest 2 cents. I'm using a PC with Windows 7 Pro, 32 Gig RAM, Quad Core, multiple SSD.
Studio One 3 & 4 ---- nice command setup, easy. Nice drag & drop instruments into the main display to create a track, easiest of all DAWs I've tried. Mixer display could use more work, horizontal spacing gap between instrument faders and master faders, didn't find it useful. Automation lanes could use some work in main display. I find automation lanes apart from their instrument track confusing. It won't fully work with my Nektar LX88+ keyboard, only recognizes my Mod wheel and that's it (I've been to Nektar's support, downloaded latest controller files, etc. Still no joy.)
Digital Performer 9 for Windows ---- not happy at all. They still need a lot more work to transplant this to work on Windows. I couldn't even record my guitar through my Apollo interface, with support from both MOTU and UAD. MOTU just quit responding to my help requests. DP is setup nice for film composing, but still a lot of things you've got to do manually that shouldn't be. And there's need for more error programming. Try to do something and hit a wrong key or command and you'll often get a crash. I suspect the Mac version is more robust, as DP came out originally for the Mac and hasn't been on Windows that long.
SONAR ---- it tried to keep up, and was a pretty good DAW. Got some of my best big band Jazz mixes on it. It still tried to process under heavy loads which degraded the audio, when it should have issued a warning. Needed some more error programming in that area. I didn't like the double tracks assignment for MIDI requirement, which is similar to Cubase.
Pro Tools ---- great for mixing. Not really bad for MIDI. It's got Step Note Entry, what more could a non-keyboard player want? PT is very robust in the error catching area. If you've got the CPU and RAM power, I find it's more stable than any of the above DAWs. Just don't expect a lot of bells and whistles like the other DAWs.