This is one area where I'm having trouble envisioning how this site is supposed to work as an SE. I suppose wrt the golfing there's an objective criteria--least characters. But for puzzles there's really not. Any answer that correctly solves the problem is technically an answer and so picking from among them seems to be impossible, objectively, unless you just grab the first one. That seems to kill the whole point of having a puzzle archived though, which would be for people to try and solve it themselves.
Even when there IS an objective criteria, someone could always come along and break the record. What are we supposed to do, set a time limit? Adjust the answer when someone comes along a year later with something better?
The problem I see here is that, fundamentally, puzzles and challenges are not questions. The person posting them may even have done it already. Very rarely does it seem appropriate to pick an "answer" to something posted not as a question, but a challenge.