What an awesome debate...what I see so far (I played each once in 7/07), let's see if my conclusions mirror Ed's:
#1s: RCD's is a gentle opener, although a good place to take a shot where you will likely be giving them back later. A saddle fairway helps straight drives go even straighter, a broad, deep green offers a chance to chip close for birdie or par. Portrush may have the OB, but this is easily one of the more devilish greens on the course. It would take many rounds to feel comfortable with this approach. Portrush 10-9.
#2s: RCD has a blind drive, and a semi-blind second, an introduction to what the player will face for much of the rest of the round. Not a hard hole, but increased challenge and interest from #1. Portrush's short par 5 second is comparable to RCD's #1 in challenge, and it also is a place to take a shot where the rough will gobble at least one later. Portrush's undulations make its #2 more interesting. Portrush 10-9.
#3s: RCD is a long hole, the first brute of the round, and the challenge has been escalated. A long drive is needed to a fairway that ends in a rise, and the green is below a marker pole. Deep, wild bunkers await the sliced fairway wood or long iron. The green is mercifully flat and open, but the game is getting there. At Portrush, we have a relatively benign par 3, but with severe trouble for the missed short iron. RCD 10-8.
#4s: RCD has a beautiful longish par 3 from one of the greater panoramas in Ireland. The entire course is below, and from here is looks like a minefield of gorse, grass-edged bunkers, and heather. The green is underrated with steep fall-offs on three sides and a bunker on the fourth. At Portrush, the fourth is one of the strongest par fours on the course, complete with centerline bunkers, interesting fairway undulations, and an attractive green set in a ring of dunes. Tough call here, a draw? 9-9. Is that allowed?
#5s: RCD's fifth is an elegant left to right par four that takes the round into some serious landforms. The drive is blind to a wide fairway, and the green is seemingly open yet exacting, with long slopes and shoulders to complicate chipping or putting. At Portrush, the fifth is on of the showcase holes. Bite off as much as you dare, if you fail your ball is at the mercy of the rabbit trails and clumps of tall grass. However, there is ample room for the conservative, if they do not mind an uneven lie to a two-tiered elevated green. Another tough call, but Portrush 10-9.
#6s: RCD plays a blind drive to a wide fairway, but the green is the showpiece here. The inverted saucer green would rival any at Pinehurst, and is one of the smallest at RCD. A techincal hole requiring an accurate tee shot (not necessarily with driver), and a pinpoint wedge. At Portrush, an attractive par three with your back to the cliffs towards the Giant's Causeway, but not one of the more memorable holes on the course. RCD 9-8.
Through 6 holes, I have Portrush 55 - RCD 55!