Logically, #20 should be the superior one. He refused to activate the others because he couldn't control them, so it stands to reason he'd be able to control #19 in case of disobedience, even if by force. The manga gives us little evidence if any, but Daizenshuu 7 does state in Gero's bio that he's superior to #19 without specifying whether it's pre or post, so it's probably a overall comparison.
As by how much, it's by enough that #19 can absorb the energy of two Super Saiyans and still be below #20.