You kind of have to go with the Redan, the Eden, and the Postage Stamp on the first team, don't you?
Don't leave out the "Eggshell" aka Dornoch #2.
I thought about Dornoch, but you could pick #6 as easily as #2, which meant I left them both off.
If you were trying to get four very different par-3's, and started with the three I named, the fourth would have to be a long one wouldn't it? I doubt there will be a real consensus on that choice since people aren't as inclined to enjoy 220-yard holes. If you want to crush people's spirits, the 16th at Carnoustie would do it, though I'd rather have another shot at the hole at Montrose that Sean mentioned. I've never seen the Winterfield hole but on Google Earth it looks like a beautiful short par-4
P.S. Cancel the above, I would go with Prestwick #5 to complete the foursome.