Everybody should own at least one G17 .
I would keep the 19, as most others said, but make sure you get good money for the 20. 10mm handguns are coming back into vogue.
I've never owned a 20 and would welcome the opportunity to pick one up.
Mike
If you are 70 and retired, keep the 19. I sold my 44 mag Ruger a while back. Too damn much vibration through my entire body. And I was 35 or so then.