A series with the score of 2-1 generally means a close set; either player could take a game off the other. In equal set wins, the player with more game wins had closer sets with the people he lost too, while more game losses means he had closer sets with the people he won over. Following the priority of ranking, set wins is obvious; it sorts by who won the most overall. If that is a tie, game wins is next meaning the player with closer sets against people ranked higher is ranked higher. If that is also a tie, game losses is next meaning the player who lost less to players ranked lower is ranked higher. If all of that is a tie, the player who won the set between them is ranked higher.
The only bad thing about head to head is that it is generally mutually exclusive with who beat the higher ranked player. In the event of a tie, the person who won the head to head lost to someone the other person beat.
For going by W/L ratio, it favors people who have less close sets with people ranked below rather than people who have more close sets with people ranked above. I think that in every case for realistic pools, W/L ratio has the same outcome as judging game losses before game wins. IMO taking games off better players is a better system, but i guess its matter of preference.