Hole #1 for me.
It sets the tone and can describe a lot of what the course will be like. The green especially.
I agree with Tom, in that the next few let the player know what kinds of different challenges to expect - either subtle, not or both.
As an example...
First hole a very wide short par 4 with a slight advantage to one side vs. the other based on the pin placement. Superb green.
Second - slightly long par 4 with a more undulating fairway, and a huge advantage for hitting the proper side, but it isn't as apparent as the first - which has cross bunkers. It looks even wider than the first too. #2 looks easy but plays hard due to the wild green.
The strategies are similar, but play quite different.