I think .tar.bz2 it's better than .zip or .tar.gz as it compresses more (specially small files ie. source code), and it's rather a very common format today in the sourceforge projects. And even for windows, most programs can open them (ie. 7-zip, WinRAR, etc).
But I've noticed that most projects on sf.net use double releases, most of them release in both formats, .tar.bz2 and .zip, and some are distributing now in .7z also.