Having just come back from there, ranking the courses, while fun, is next to impossible. All 4 are so good that you are picking hairs when you distinguish between them. Also, they are so different that each has its strengths.
If I had to play 1 course every day, it may be Bandon Dunes, as I think it is more forgiving then the other courses. You can miss shots and not get killed.
If I could go back and only play 1 course, it would be Pacific Dunes. There really is not a bad hole and it requires you to hit good shots.
The most unique golf experience there is Old MacDonald (unless you play NGLA frequently). It just has some really fun golf shots - I want to play #7 again more than I want to play any other hole at the resort). I really loved playing 3, 7, 8, 12, 14, 15, 16 and 18. Just fun golf.
The best test of golf is probably Bandon Trails. It really rewards good shots and punishes bad ones. Wind is usually not as much of a factor. However, as someone in my group said - BT is a great golf course but I can find comparable courses in the midwest. I cannot get the other 3 anywhere close to where I live.