It is not really direct answer to your question, but I think complete (database plus files) backup/restore is more comprehensive and important.
Content backup is only content. Database is all of your blog, which can help you go from nuked database back to normal in no time (speaking from sad practical experience, that would be much more sad without complete database backup).
Would you like to keep your question about clients alone or expand it to backup/resotre in general (it’s marked as community wiki so I am trying to establish scope) ?