I've been using recording software for the last 17 years and I have yet to see an OSS competitor to Sonar, Logic, Protools, or any of the big name commercial packages.
Reaper is the closest I've seen as far as projects with a seemingly smaller budget go, but it is not OSS. Ardour is decent, but you're going to want good virtual instruments and quality effects if you want studio quality recordings. So you get Ardour for free, but you'll still want to use Native Instruments or one of the other solid VST modules for effects and those are never cheap.
I'm guessing your basic needs are multitrack recording, mixing, editing, effects processing, and MIDI/virtual instruments. Ardour does those very well, although it was a bit unstable last time I used it. I was using it as a VST host and if I recall correctly it didn't like the 96Khz samples I was using.
I ended up purchasing Sonar used from a craigslist ad and paid about 1/6 of retail.