x2 on the USB Ethernet adapter. When I used Migration Assistant from my old MacBook Air to my new one, I had about 50GB of data. Over Wi-Fi it would have taken over 20 hours. It took about 3 hours over ethernet.
One option that might be cheaper than getting the USB ethernet adapter (Apple's is $29) is simply to use Migration Assistant to move only your user name and settings, and to copy over your Applications folder, Library, and data folders separately. To do that, take out the MacBook Pro's hard drive, get a USB hard drive enclosure from an online retailer for about $10, put the Pro's hard drive in it and connect it to your MacBook Air's USB drive. Copy over what you need, then put the hard drive back in the MacBook Pro and you'll be on your way.