Rsync beats using SCP if you’re trying to copy files from one directory/machine to another. Definitely use rsync if you already have a partial copy and want to copy only new/changed files. This will save you having to copy any files that already exist and are the same.
E.g.
rsync -avz user1@machine1.fqdn:/source/directory/with/all/the/files/* /target/directory/
The -avz options are [...]
Continue reading about Rsync usage and ‘Argument list too long’ error