Regarding the Castle Course, 16 and 17 are both fairly strong, 17 especially, but I'm not a fan of 18 myself, the setting is fantastic but I find it to be a really forced and rather strange hole. It would be much better imo if the tee was further left on top of one of the big dunes/mounds. It would open up the angle better offering bigger hitters more chance to take on the narrowed section of the fairway at the corner, which at the moment from the current angle is almost impossible to hold and therefore really limits the strategic options of the hole. It would also let you see where the cliffs on the corner are, currently you can't really see the cliff edge on the right of the landing area and the hole doesn't really gives you anything to aim at from the tee. I find it very disorientating and can imagine first time players really struggling to work out what is going on, not realising that they should be aiming what feels like miles left. The tee being higher would also give you a great view of the whole hole set out in front of you. making for a spectacular climax to the round.
As for good finishes I would go for:
St Andrews (Old)
St Andrews (Jubilee) - from 15-18
Carnoustie
I also like Ian Andrew's suggestion of Commonwealth too, not one that would initially spring to mind but they are three of the strongest holes on the course, 17 is a great little hole.