What a great thread - thanks!
First, it strikes me that the "return to the clubhouse" requirement is, more often than not, a handicap. What if the terrain approaching the clubhouse is totally ordinary? Or what if the opportunity to build truly great 14th-17th holes leaves nothing left over for the architect to work with?
I favor really strong par 4's as finishing holes that demand a long iron from the normal good amateur and at least a 4 or 5 iron from the very longest (mortal) hitters. I also like the 2nd shot to require a carry to, at least, the front of the green - a "heroic" shot, if you will. Therefore, hazards that have to be carried are OK by me. Also, the tee shot needs to be long and reasonably straight to set up the approach. In short, 2 darn good shots by a good player are required to reach and hold the green - playing safe for par just isn't an option. Also, making bogey after a poor shot should be difficult. I acknowledge that, since birdies are scarce, my ideal 18th may not be the most exciting hole if David Toms is chasing Tiger and needs 1 more birdie to tie. Can't have everything, I guess.
My favorite is Merion, even though only the drive has to be "heroic" and carry a hazard. The second shot is unlikely to run up the slope in front of the green, though, so a full 195-205 (slightly uphill) carry is required to reach the putting surface. I'm not sure of my second favorite although TPC Sawgrass is certainly in the running. Southern Hills also made an impression although it's been a while since I've played it. Can anybody opine on whether Carnoustie would fit the profile? Winged Foot West would be another possibility although that hole's just long and hard without much heroism required - to me, at least. I've never played Medinah but I'll bet it's similar.
I think #18 at Pine Valley is a wonderful hole but I've seen many mid irons, and even a couple short irons, played there in recent years. Is it still tough enough after a good drive these days? It certainly filled the bill through the 60's, at least. Hitting 2 and 3 irons across that water and those bunkers - wow!
I'm not a fan of even the best par 5's - playing safe for par is just too easy. Does that mean that Pebble #18, as great a strategic hole as it is, doesn't fit my criteria? I'm afraid so.
Finally, even really great par 3's aren't my favorite although every par 3 18th I've ever played was quite good - I guess they have to be to get away with it. I know there was a thread in the last couple of months on this so I'll leave it alone here.