Nate is the annoying Diaz; Nick's not only a better fighter, but a more enjoyable one to watch. If Nate can't get a submission locked in, he loses. He has no real striking, has no real power, has no real strength, no wrestling...I'm sorry man. If you like him that's fine, but really Nate reminds me of a possum because he plays dead and then goes for submissions and that's it. It's hard to feel bad for him when he loses.
Nick on the other hand has KO power, is a decent striker, excellent chin, way tougher than Nate, even better Jiu Jitsu, and I love the guy. If this was Nick fighting Melvin I'd root for him all the way.
With all of that said, I'm gonna call Melvin for the upset win. Nate won't take him down, and unless Melvin becomes dumb and tries to fight on the ground, Nate won't be getting a sub otherwise. Melvin wins by either KO or decision.