Connors at the USO:
5 titles, 2 finals, 7 SF, 3 QF. From 1973 to 1991 he missed only once the QF or better.
Sampras:
5 titles, 3 finals, 1SF, 1 QF.
Federer:
5 titles, 1 finals, 2 SF, 1QF. His titles were consecutive.
Lendl:
3 titles, 5 finals, 1 SF, 2 QF. He had the same consistency than Sampras, but struggled to win it.
I would say that Connors is the USOPen Goat by a good margin. He was a factor here for a freakin 20 years! Behind him Sampras and Fed are tied. Fed as the consecutive titles while Sampras has more finals. Fed is not done though. Lendl is not in the discussion, as he couldn't win the last match.