If you're just talking about one or the other:
The best starting par-3 I've seen is The Berkshire (Blue). I also like the 1st at Kilspindie for an opener.
Finishing par-3's are more common. The best, for me, is the 18th at Garden City, Walter Travis' version of an Eden hole. Pasatiempo's is good, but they don't get to use some aspects of the green at modern speeds.
I have yet to build a course with a par-3 opening hole or finishing hole. Clients have had something to do with that . . . at Stone Eagle, I wanted to use the 19th hole for either the 1st or 18th, but they just couldn't bear it. [The client was a development company; you have more chance of convincing an individual.] As mentioned, the 1st at The Tree Farm will be a par-3, but I only get partial credit for that . . . I had drawn it as an alternate on my original routing, and Zac liked that alternative better than the other choice, which was a par-5 all the way to the 2nd green.