Evan:
I really dislike both of your choices. The Prince's opener offers a good chance for a lost-ball start, and the hole at Bethpage is a long drive to a flat fairway with trees blocking the view toward the green.
Most of my favorites have been mentioned: Machrihanish, Long Cove, National Golf Links, Sand Hills, Mid Ocean, Garden City, Crystal Downs. Lost Dunes and Stone Eagle were the only two opening holes I've built to get a mention, and they are probably my two best.
I have built several par-5 opening holes but if it weren't for all the other factors involved in doing a routing, I would avoid par-5 openers where possible. Unless you build an easy green complex you are raising the possibility of a six to start the round, and I hate making a six early in the day. That opening sequence at Black Forest turns everyone off ... the first two are really good holes, but at that point in the round you are just not ready for them, and it's way too easy to start 6-6.