I created this question in a similar vein a while back in a bid to stop it being asked sloppily and as something of a seeding experiment. The results have been perhaps encouragingly underwhelming and after 8 answers (half of them from one user) and a sum of +3 upvotes, it is clear that the search for maths puzzles is not about to take over the site. Indeed the last answer was getting on for a good two weeks ago.
The question under scrutiny is perhaps similar and with a total of no upvotes it is unlikely to be around for long, at worst barring sporadic answers bumping it to the front page once in a while (something that would not be the end of the world for me at least- I know some people at MO defend the front page with their lives though, so who knows...), and as a temporary crowd pleaser that survived a while on MO, I feel there is good precedent to allow it to survive here a while.
In addition, I do not consider it the first of a slew of questions: "favourite X" only has rational solutions X= puzzles, formulae, theorems, quotes, jokes and papers (at a pinch) [perhaps there are, maybe, 3 others but] you get the point- once these are out of our collective system, anything else is [closed as exact duplicate] or interesting or closable for other reasons.
Finally, I will admit that I added a quote, and I may add another. I may check this question occasionally, in case someone adds something that really interests me- but you know what? No harm done.