Neither.
I mean, I suppose that if I had to choose between only these two, and specifically with gaming in mind, I'd pick the buckling spring, since the tactile and auditory feedback of BS is more precisely aligned with the activation than, AFAIK, any other switch, but I'm not super enthusiastic about either BS or MX Green.
Of course, if you do go the BS route for a gaming keyboard, you will have to work out a way of implementing acceptable rollover, unlike Unicomp. An NKRO membrane (there are a couple of Korean market dome keyboards with this) or Model F-style capacitive sensing would do. A "gaming optimized matrix", on the other hand, is not acceptable, since these are just 2KRO with marketing bull****, even if they claim a large rollover number by measuring incorrectly (rollover is measured by the worst-case scenario, not the best).