GNOME's new Files app (Nautilus) has been a bit controversial. While the devs have admitted that they should have followed GNOME's feature proposal process and the UI had some obvious bugs in the 3.5 snapshots, I think Nautilus 3.6 is a clear improvement for most users.
I believe that nautilus 3.8 is the best choice as default file manager for users and for Ubuntu developers for 13.04. I just don't see anything else that has the stability, shared maintenance, and integration with the default desktop that the latest nautilus has.
We should come up with a list of specific requirements that we want from Nautilus which we can present to developers. Here's my start: