Totally different scopes.. A vx6 is a lightweight hunting scope that prioritizes weight reduction.
Everything in the nightforce line is designed to be used as a hammer, in case you can't find yours. Look at the weights. If you want to drag your rifle up a mountain, take the leupold, if you want to walk out 50y and set it on a tripod, take the nightforce. To make a realistic comparison, in the leupold line you would want the mark V, VI, or VIII.