upgrading domain & exchange - which to do first?

We are currently running a Server 2003 domain & Exchange 2003. We are planning on upgrading both this year to a 2008r2 domain & Exchange 2010.

I've done some looking & it seems that either upgrade can be done first; both configurations are supported.

http://technet.microsoft.com/en-us/library/aa996719(EXCHG.140).aspx
(Exchange 2010 on 2003 domain)

http://technet.microsoft.com/en-us/library/dbac2d40-da8b-469f-a265-1d1f948fe446(EXCHG.141).aspx
(Exchange 2003 on 2008r2 domain)

Are either of these upgrade paths "better" (& why)?