I have SPlat, Reaper and Audacity installed. I prefer SPlat because of it's workflow (particularly mixing and comping) but Reaper is far more stable and does certain things better like time stretch, MIDI mapping, etc... (although I'm still learning it). Audacity it's just something simple to use and has some interesting tools/options for general stuff. It's good to have options.
I am considering getting Cubase Elements to see if Automation and MIDI is better and I'd like to have reliable MIDI scoring (not sure if Elements has the scoring stuff though). I started on Nuendo many moons ago and it was decent. I've been checking out modern Cubase vids and honestly the way things work now seem kind of annoying compared to Sonar but I know there'll be some useful items in it. It will also allow me to collab with studios using Cubase (most studios will have it even if they're Pro Tools based). Extra FX and instruments are always welcome too.
I've never liked being forced to use dongles but Elements doesn't require one and it's only $100.
Don't think I'd really want to spend money on SI because it sounds very similar to Sonar with a few extra options but other things missing. That money is likely better spent elsewhere.
I am curious about Bitwig. It looks like it does some INSANE stuff but outside of my usual genres (seems very electronic music oriented).
I've got an old copy of Ableton Live LE on disc I've yet to try.
PT can go pound a lemon.