Dan:
I suspect that a lot of architects think the 18th hole is most important, and because of that you are often bored to death by the time you get there.
One hole doesn't make or break a course, so there is no one most important hole.
That said, one of the theories Mike Keiser has about the flow of a golf course is that if you can put a couple of highlight holes spaced properly through the round, you can get away with lesser holes on either side of them because people are too busy remembering the star attraction. He came up with that theory when we played Portrush together back in 1995 ... and you can see its application at Bandon Dunes and Pacific Dunes, with the highlight holes coming at similar places in the round, and NOT at the end.
Personally, over the years I have come to believe that the starting 3-4 holes are more important than people (including Jeff) give them credit for ... if you haven't made me fall in love with the course by then, you're probably not going to get me.
I take the fifth! (As in I would be happy to move the "dogs" (or pussycats) no closer to the start than the fifth!) Actually, I know that in making speeches/presentations, speakers either grab an audience in the first 17 seconds or lose them forever. I don't know what that translates to in golf terms, but I figured the first hole, or maybe the second at best.
I also agree with Tom that flow is more important than any particular hole, and when talking about "getting holes right" we might be talking visual, play, or most likely a combination of the two, and their context within other holes.
To grab a player, you probably want to get them off to a good start, and also have some good visuals on the first hole (or two). That is by no means a formula, but many people do like a benign first hole. I am also conscious of providing a few easier holes throughout the round, and the possibility of double starts, so the "ideal" w/o land considerations, and considering overall flow, the placement of slightly easier holes might be 1,5,10, and 15, as an example. (It rarely works out that way and some courses are memorable for their difficult or great first holes) As Tom notes, harder or more spectacular holes might be just ahead and a few holes behind those, at least in theory, and I have always believed in easier or memorable 18th holes, like reachable 4's or 5's in place of the long hard 4, but have some of each in my work.
I think he would agree that you work each individual hole until you think its the best it can be, as I said in my first statement, knowing that we can't control perceptions and they aren't universal (i.e, the 6th just doesn't fit my game).
So, some golfers will find any particular hole more or less pleasing than others.
But, I don't mind thinking in terms of general theory! That is, after all, what we are here for, no? And, as gca's, we really don't start with a totally blank mental canvass - it helps to have some idea of why you generally MIGHT do something given any particular set of circumstances - i.e., try to avoid five tough holes in a row, so you tone down the features on two of them, etc. Or, better yet, tone down one type feature on the first of that sequence, say bunkers, and tone down the green on the next, etc.
As I preview this, I can hear the howls coming, although for the life of me, I can't imagine why. If we talk about flow, then a gca MUST eventually think about it in very specific terms, rather than the generalized "go with the land", etc.