2010 is the most innovative and the one to which all rights will pass within some time.
being just out is not said to be immediately stable (it is all to be tested) so 2009 ( theoretically) with the next 5.0 service pack will be at full maturity.
If you have to learn and then you have time before using it properly I suggest you leave with 2010, if instead you will exploit it immediately begins with 2009 for work and installed a 2010 to try it and test its reliability.