I have tested with both Ancestry and FTDNA and Ancestry has been by far the most useful. I have 250 fourth cousins and closer on Ancestry and almost 10,000 total matches there, even after The Great Purge this summer. I have been able to identify the relation on almost all of my 4th cousins and closer with the aid of Ancestry's 'shared matches' tool and family trees. On FTDNA, other than my brother, I have identified exactly one person where I could figure out the connection. One.