I'm very partial to Nikon scopes. VERY good optics and the mechanism is true and reliable. My 22-250 has a Monarch UCC 6.5-20x44AO on it that is clearer at 20x than my Bushnell Trophy at 3x. I've sized up many Leupolds, and while they are good scopes to be sure, I just don't think they are worth what they get for them. The Monarch UCC easily compares with the Vari-X III's and is much cheaper. However, I don't think that you could go wrong with either brand. I just think that Nikon definately has the edge on optic design and lens coating techniques (95%+ light transmission on the UCC scopes!), probably because of their extensive research and experience in the camera and scientific optics field.
My Sako 75 7mm STW will also wear a Monarch UCC 3.5-10x50...I can't wait to get that rifle, either!
IMO, you're going to get more for your money with the Nikon, but if you really like the Leupold or are dead set on "buying American," then I doubt you'll be unhappy with a mid- to top- end Leupold.
Mike