Shane -
I played one round on each course in 2000. I believe some changes have been made on the back-9 of Royal Aberdeen since then. I think a few holes on the back-9 at Cruden Bay have been changed since then as well.
If you are looking to play a classic, straight-forward, links course, I would recommend Royal Aberdeen. If you are looking for quirk, unusual holes, blind shots, etc., I would recommend Cruden Bay.
DT