Given the new look at Oakmont it would be exceedingly difficult make the comparison with Winged Foot or with Oakmont Opens past.
I would have no idea how to rank the ten toughest US OPen sites except to say that WF, Oakmont, Shinnecock, Congressional, Olympic, Southern Hills, Oak Hill and Oakland Hills would all make the list. Medinah, too, although it may never host again. Ditto Brookline. Pebble if the wind blows.
Trees play a huge role in every course except Shinny and Oakmont (now).
My guess is that Oakmont will prove to be a very tough venue. Any course is subject to a 63 at that level of competition.
OK, I'll try-
1. Winged Foot
2. Oakmont
3. Shinnecock
4. Oakland Hills
5. Olympic
6. Medinah
7. Congressional
8. Southern Hills
9. Brookline
10. Pebble Beach