It always seemed to me that StackExchange's own http://programmers.stackexchange.com was intended for this very concept. From the FAQ:
What about subjective questions?
Subjective questions are allowed, but subjective does not mean “anything goes”. Please keep it professional at all times. If this is a question you'd be uncomfortable discussing with your colleagues in a work environment, it's probably not appropriate here, either.
For example, here is a question re: CSS pre-processors that seems pretty subjective: http://programmers.stackexchange.com/questions/181536/are-th...