If I follow the implied guidelines suggested by your examples, than I would say that I'd go for the working keyboard. The non-working one would drive me crazy. If I can't fix the problem, I'll sooner destroy the keyboard attempting to do so than I would accept living with the problem.
I should note, though, that this answer depends on certain boundary assumptions...that is, when you say "least favorite keyswitch" that you are only considering switches that, at the current time, are common in mechanical keyboards. If "least favorite keyswitch" includes every switch ever made by any modder or company at any time in history based on any kind of technology, I might be persuaded to reconsider.