Had to vote for the SO, even tho a unique situation.
Otherwise, my best sex has uniformly and consistently come from providers.
The SO was in college. Once we got together, she fucked my brains out several times a day on a daily basis. So often, my cock got raw and it was painful to fuck. But she still attacked me, not giving me much time to recover. She satisfied my youthful lust and no other woman ever did. The down side was that she wasn't very experimental with her sex. It was basically normal positions and fucking so hard we were slippery sweaty when we came. Give us 15 minutes of recovery and we were at it again. It was a time to rut.
My current SO is very vanilla. And I'm kind of a freak. So there is something missing that I can only pick up in the hobby.