Sharing would probably be the easiest way. Share the files you want to transfer and then browse to \\<computername> or \\<ipaddress> and access the shares. You will probably want to create a seperate account just for file sharing that has permissions only on the shared folder that you can disable and reenable as needed.
File sharing for sure, however make sure you don't place either one of those computers on the internet with the sharing enabled. That's a big welcome mat to less than desireable folks.