Pixie is a big advantage for the X team, specially when bloodlusted. Hazmat and Veil would be the most dangerous otherwise, but they are outgunned here.
X-Men. Striker is the only one that can do anything to Mercury, and he is completely canceled out by Surge being a giant lightening rod that will absorb all his energy. There is nothing the Avengers can really do to Dust and Mercury and Pixie magic, hallucinations and soul dagger just tip it even farther towards the X-Men. This is really a huge mismatch IMO.
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All in all, I'll go NXM. Dust and Mercury are big threats, and the team overall has better teamwork. I think the AA have more power, but they're facing a team of people who trained wanting to be heroes, and who've been around the block a few times by now.