Depends on what you want to do.
For example, the overhead on FTP for fetching a list of files is 7 bytes (LIST -a), while it's 370 bytes with Webdav (PROPFIND + 207 Multi Status).
For sending some file, the overhead is lower on FTP than on Webdav, and so on.
If you need to send/fetch a lot of small files, FTP will prove faster (using multiple connections for correct pipelining, and per-file TCP connection).
If you're sending/receiving big files, it's the same on both technology, the overhead will be negligible.
Please see:
http://www.philippheckel.com/files/syncany-heckel-thesis.pdf
