It's a toss-up.
NFS, with the right setup, version, and tuning, is just a tad slower than SMB/CIFS. Older versions, however, can be significantly slower.
What you do gain with NFS is:
- primitive file access control (via standard Unix file permissions)
- primitive share access control
- user mapping
- For those platforms that support it, a near-invisibility with regard to operation. It looks just like another subdirectory...
However, if you are not working in a 100% NFS environment, you might find that it's not worth the effort.
By the way, for the record, Windows 7 Beta/RC does support NFS out of the box.