For the purposes of my response, I'm going to assume you mean the Warne XSkel Gen 2 Extended MSR mount...
I too considered both of these mounts for my AR, which will be used mostly as a calling rifle as well as for varmints. Ultimately I ended up going with the Aero Precision Extended mount because of the weight and all the praises I've seen regarding them. It is a great mount, built in the USA by a reputable company.... but in the end, if I had to do it over again, I would have gone with the Warne, simply because of the additional hassles encountered trying to keep the scope level when mounting my scope with the Aero.
If you don't use a scope leveling kit and simply eyeball your scopes reticle for level, or you take it to someone else to do it, I'd say go with the Aero. If you like a less painful mounting experience, I'd go with the Warne - also made in the USA by a reputable company - because it is only 3oz. heavier, just as good, and it is pretty hard to screw up mounting a scope level (using a leveling kit) on optic mounts that use horizontal mounting brackets vs. the vertical cantilever-style of the Aero Precision.
As mentioned, you will read all sorts of praise regarding the Aero Precision mounts on this forum and elsewhere, but the only negative feedback seems to relate to the problem I was describing: keeping the scope level. Ultimately I ended up having to set the scope off-level 1-2 degrees and then tighten the screws on the cantilever-style mounting clips. This pulls the scope to level, but this process definitely took some trial and error and more of a hassle than I want to deal with again.
My $0.02