The current one, whichever it is. The music of previous decades are still there if you want it but you also have the present and the first inklings as to what the future holds.

For example, in the 1960s you had great music of all kinds appearing on both sides of the Atlantic. In 2009, the music of the 1960s (or whenever) is still around through vinyl, CD reissues, previously 'lost' recordings, boxsets with extras that never saw release originally, as well as material that had a very limited release or appeal initially and wouldn't have been heard by many people even at the time.

There's particular aspects of music I like more in any given decade, but as someone who is genuinely interested in music per se, I benefit most from the decade that offers me more and 2009 appears to offer me more.