Well, now there's word from the National Association of Good Grammar that "twenty ten" is more correct.
NAGG's founder (and sole member) was quoted in the Chronicle:
The "20" should have been pronounced "twenty" all along, he said, pointing out that every year in the 20th century was pronounced "nineteen something."
" 'Twenty' follows 'nineteen.' 'Two thousand' does not follow 'nineteen.' It's logical."
I guess that makes sense, though I think both ways are probably okay. For me, it comes down to economy, and "twenty ten" is fewer syllables.
For that reason, BuboBlog hereby endorses "twenty ten" and pledges to use it exclusively in all its official business.