I have Sand Hills 1 up after 14 holes.
My memory of each hole is sketchy. The long iron or fairway wood shot into each hole is very enjoyable. Both have big targets, though the front right bunker at Riviera's 15th green guards the right side of the green too well for my game, so I will almost always be chipping down to the pin from the left rough.
I'm going to go with Sand Hills here. In comparison to Riviera's 15th, I think that the Sand Hills hole is multi-dimensional, with far more possible results. I think it would be easier to make a 3 there, and easier to make a 7. If you played each hole 100 times, you would experience far greater variety in the nature of your experiences at Sand Hills, and the quality of the shots at Sand Hills is not significantly less or greater than the quality of shots at Riviera #15.
Sand Hills wins, and goes 2 up with 3 to go. Oh shit, how am I going to manipulate this to make it exciting?
To preview, I see Sand Hills winning 16, Riviera winning 17, and Sand Hills winning 18. Wait a minute; I've figured it out. I'll make 16 a draw.