both offer attractive congestion control scaling properties that, if adopted by Urbackup, should result in increased throughput when performing backups.
SCTP also has nice features like
multi-homing, which can allow automatic failover if an interface goes down, such as a laptop moving from wifi to ethernet
multi-streaming, which can allow multiple simultaneous streams to live independently inside an SCTP connection. Possible uses would include a stream for control, and another stream for transfers, or for file backups Urbackup could open a new internal stream for each file to be backed up, up to some limit.