gpl v2. Let's avoid "or later" until that controversy is resolved.
I don't see a problem with "v2 or later". Everybody who doesn't like to use GPLv3 (when it's released) can just chose to use v2. That's perfectly legal.
FWIW, no one but the original author(s) can decide to re-license "v2 only" code to "v2 or later" (later licenses [can] include extra restrictions, which are explicitly not allowed by the v2 license).
Segher