Having played over half of Oregon's fine set of courses and the bulk of the courses in the discussion for the top courses, it's a tough call, in all honesty, Oregon doesn't, in my opinion have a definitive 5 star course in it's year round condition. All of the top courses have at least some flaw that keeps it 4.5, that being said, we have a nice number of 4 and 4.5 star courses with which to romp around on.
I'd say that the best course in Oregon, in my opinion judging on quality of golf, is Milo in its 36 hole BSF layout, with the course fully marked and all the pins in what I would call their "marquee" pin locations, it's an absolute stunner of a course, albeit difficult and long enough that it might frustrate newer players. Milo's 36 layout stands out as a top notch 5 star course, Ken Climo himself remarked that it was in his personal top 2 nationwide.
I'll second Eric's comments that Trojan should really be in the picture, its rating on this site is rather unfair because many of the ratings came before the course was, in all honesty, finished. I also think some of the flak comes from how frustrating it can be to newer players with more than half the holes holding a serious risk of losing discs in the water. The course should be thrown up there in part because of its true test of golfing ability, the course is amazing in tournaments, especially when it's lengthened for the pro divisions.
I definitely love the work Bob Horning has done on the new Meadow ridge course, and it certainly ranks as the best disc golf "destination," that being said, I don't think it's as good as the ratings attest, as far as a stunning impression, it will definitely have that effect on players, but the course itself has a few flaws, the baskets being one of them. And personally, I can't see myself wanting to play it as often as a few others as it is very draining, technically and physically, and it has a higher luck factor, in my opinion, than Pier or Milo.
I could say more about the other top courses, but I don't want to write all day long.
My personal top 5 (largely based on personal enjoyment factor)
1. Milo
2. Pier
3. Trojan
4/5.Horning's Meadow ridge
4/5. Whistler's
Dabney and Timber are both tremendous courses I play frequently, what keeps them off the list for me is the lack of the "wow" factor, those big challenging holes that crank up the excitement level for me Those two as well as Horning's Canyon and Adair would all line up as number 6 on my list.
The only course I can think of that's up there that I haven't played yet is Dexter. Finally, I would give a nod to the Mt. Bachelor Alpine course, I've only played it during the Lava Launch tournament which souped up the course and added another 9 holer down the slopes, but that was one of the top disc golf experiences I've ever had.
