I've been using REAPER since about 2008 or so.
Both on OSX and Windows. Never did record anything on Linux, but it was so long ago that I ran Linux that it was pretty much impossible to do anything back then, really.
I also use Audacity for minor administrative stuff (mostly encoding finished mixes etc).
I've tried pretty much every DAW out there, and nothing even comes close to REAPER, especially considering it's "free" (evaluation version with only a nag screen as the deterrent).
Also available for Linux now. Couldn't recommend it enough.