Neither of these are great, but both decent enough. I'm not a fan of megas, but everything new except Yveltal is good in gen 6 Flying. Meanwhile, I don't really like the gen 7 legends, but Mimkyu, Primarina, and Ninetales are all great, better than anything from gen 6. Think it's a narrow win for 7.
Perhaps the golden rock was inside us all along.