I personally would go with TG2 (but would also look at other frameworks such as Pylons or repoze.bfg) esp. if it's a new project. Remember that you might need to upgrade at some point (or want to at least). TG2 also is offers full WSGI support which gains more and more traction and is IMHO also something you really want.
For me the most important thing these days is always how good the code of that framework looks like because you never know when you need to dig into it to try to understand some misbehaviour or even fix a bug (regardless of what version).
Another important aspect is IMHO the community, so hanging around in IRC channels or on mailing lists for a bit might help you to make better decision.
Maybe these 10 reasons to use TG2 also help.