Shawn Blanc has written an extensive, yet great review of both new Coda applications. He correctly notes one of my few quibbles with Coda 2:
Coda 2 does not support Lion’s auto-saving and versioning for local files.
I love auto-saving, and I can’t see a reason this was omitted. Overall, though, Coda 2 is an application you will want to open on a regular basis. It does the impossible: it makes writing code fun.