Joe:
I'd go Oakmont, Shinnecock and Pebble Beach -- maybe not in that order, but maybe; it's hard for me to distinguish which of the three is the best US Open test, because they offer different tests.
Shinnecock is about as linksy as a US Open will get, particularly if the wind is up as it often is in June out there. Players just don't see that type of US Open set-up that often -- extremely fast and firm (sometimes too much so
), and it remains a great test of golf. I'm fairly convinced (my own little theory...) that the re-introduction of Shinnecock to the US Open rota in 1986 set off the interest here in finding land that could replicate what Shinnecock offered in terms of a links-like experience, and thus we saw the development of Bandon, the Nebraska Sand Hills courses, et al.
Pebble is on my list because it has about a half-dozen of the very best holes on the planet to test the caliber of US Open players. And it's just great looking on TV, a factor for me at least. I also don't think you can divorce the typical conditions of Pebble in June from its worthiness as a US Open venue -- Pebble in February is very different than Pebble in June, and the very fast and firm conditions you get there in early summer are part and parcel of its appeal (to me) as a US Open course. To me, Pebble is the one US Open course where conditions can get right on the edge -- and sometimes topple over -- in terms of severely punishing the best players on the planet (like the final round in 1992, when no one shot under 70).
But Oakmont is also the one course that, hole after hole, epitomizes what the US Open should be about -- a very difficult test, where par is an accomplishment, birdies come about because of exceptional play (not some shrunken, option-oriented Mike Davis bastardization of a hole), and bogeys are likely with even the slightest of misplays or mis-judgements. It can be set up to be very penal, with little relief, and greens that confound everywhere. It's what a US Open course should be like.