@mdhughes @aral The FOSS devs oftentimes use GPL and are perfectly happy to introduce GPLv2+ code, and the indie devs can use GPL code too and even sell their software as long as they also give source and GPL rights as required. Ardour does this and it works pretty well for them.
I will say, though, whatever GPL version you choose, please, I beg of you, add the "or any later version" clause or you give license auditors and devs a headache. I have had some interesting messes to untangle because of the lack of "or any later version" clauses when trying to piece together a program.