Bittorrent. No, really. Lots of nice behaviors when transferring large amounts of data between arbitrary endpoints. Transferring the torrent metadata is pretty trivial and can be done via a wide range of methods, and having that flexibility can be nice. Unlike HTTP, you get reasonable retry behavior on network hiccups. Also, more robust data integrity guarantees, though a manual hash test is probably a good idea eith…
Seriously. Zmodem/resume was doing better in 1986.