I am having the same problem - choppy playback on Audacity 2.0.5. I use a Mac Pro and the OS X 10.9.1. I’ve not had the problem with Audacity 2.0.3. It began showing up on 2.0.4, so I just went back to 2.0.3. Now 2.0.5 still has this problem with my system. Back to 2.0.3 again, which has worked great for me.
I am playing 24 bit/96kHz uncompressed .aiff sound files. They play fine using the Finder “Quick Look” feature. They also work fine in iTunes.I don’t know what to set the buffer to. It all worked fine in Audacity 2.0.3.
I have not tried recording with this new version yet. First I want to make sure it will play back, and so far it has not.