> witch is the best lossless video codec that ffmpeg/ffmpeg2theora  
> supports?
I'm sure that's a matter of opinion, but if you're asking on this
list
I'm sure you'll hear Theora, for the obvious reasons. It does have  
it's own issues to address, though. xiphmont which are supposed to  
become version 1.1.
http://web.mit.edu/xiphmont/Public/theora/demo.html
http://web.mit.edu/xiphmont/Public/theora/demo2.html
http://web.mit.edu/xiphmont/Public/theora/demo3.html
http://web.mit.edu/xiphmont/Public/theora/demo4.html
http://web.mit.edu/xiphmont/Public/theora/demo5.html
> Is it worth using dirac yet?
http://diracvideo.org/wiki/FAQ#When_will_Dirac_be_ready.3F