When transferring large files your first choice should be rsync, since it gives you the ability to resume unfinished/dropped transfers. However, if you started a large file transfer with ftp/sftp or scp and the connection was lost during the transfer, you don't need to start over again. Simply run rsync the following way and it will resume your transfer :
rsync --partial --progress --rsh=ssh <USER>@<HOST>:<REMOTE_FILE_PATH> <LOCAL_FILE_PATH>
This command is what should be used for large file transfers.
