Absolutely not 3.0 - 3.1 is out and is stabler, better, faster in every respect; it makes absolutely no sense to start with 3.0 at this time, if you want to take up the 3 series it should on all accounts be 3.1.
As for 2.6 vs 3.1, 3.1 is a better language (especially because some cruft was removed that had accumulated over the years but has to stay in 2.* for backwards compatibility) but all the rest of the ecosystem (from extensions to tools, from books to collective knowledge) is still very much in favor of 2.6 -- if you don't care about being able to use (e.g.) certain GUIs or scientific extensions, deploy on App Engine, script Windows with COM, have a spiffy third party IDE, and so on, 3.1 is advisable, but if you care about such things, still 2.* for now.
