Last 2 mountain stages in 2015 are up there for meVery fair points.
That first Alpine stage yes, I can't think of any recent Tour mountain stage since that comes close to it. But the second Alpine stage from 2011 in hindsight, is maybe overrated. It was incredibly exciting straight from the start, which almost never happens, but once it all came back together at the foot of ADH, well, there wasn't a huge amount that happened on the final climb was there? I welcome having my memory refreshed, but by that point in the stage it seemed fairly obvious that Contador couldn't pull back the sort of time that he needed, and because Schleck had already exerted himself so greatly early in the stage (as well as on the stage before obviously) he didn't really have much left to throw at Evans, and the destination of the yellow jersey was as good as decided. What I am suggesting here, is that Contador did attacks later in Tours that were also exciting. I guess those attacks didn't last quite as long in 2015 and 2017, but were they really that much worse (or less exciting) than his attack in 2011?
Maybe AX3 2013 can challenge that stage as the second best Tour mountain stage in recent memory? The first half was probably very boring, but then Quintana attacked long range on Pailhares and got a decent gap at one point. And there was the build up of a first confrontation between Contador and Froome at the Tour, and at the time a lot of us didn't really know how poor - by his standards - Alberto would be. And as we saw, there was action galore on the final climb. Perhaps the definition that I am looking for is "dramatic" mountain stage, rather than "best". Anyway, since that 2013 stage, I don't think anything else comes into this discussion (though last years shortened stage 'could' have).