Why would you ever prefer a wireless connection over a wired connection. The wired connection you probably needed to manually connect the hardware, indicating there's a good chance you want to use it. The wireless connection is probably your neighbors' unconnected wireless access point.
This is yet one more thing that NetworkManager seems to do wrong--worse, telling it to disable wireless while it's trying to connect to one doesn't cause it to fall-back to the wired network; that only happens if it sees another cable inserted (i.e. unplugging and re-plugging the cable in).