The second one (personal openion)! That seems a bit darker but more close to the Ubuntu orange (as specified in Ubuntu's Brand Assets). While the other one is far from this (but seems that's what recommended by Jono Bacon, Ubuntu Community Manager, in his website as linked by Oli in his post) and looks somewhat a blend of the community-feel Ubuntu Orange and commercial-indicating Canonical Aubergine, and may be that's the intention - cover both community and commercial software packages with that shade!
1: Ubuntu Orange - Canonical Aubergine blend:
2: The colour palette:
snap2 http://design.ubuntu.com/wp-content/uploads/ubuntu-colour-tints.png