What sort of targets are you going to be shooting at? The smaller the target the more magnification you can use. Although variable power scopes are more flexible, a fixed power scope could do you. It will depend on your type of shooting. I prefer a variable power scope. I'm running at 2.5-10X on my AR and a 5.5-22X on my .308. When I practice, i shoot at 1/2 MOA targets, so i like magnification.
As a general matter, I like the Nikons better than the Leupolds. The glass is good and the eye relief doesnt change when yoh dial through the magnification range like it does with Leupolds. Although I'm a Nightforce fan, I'd look at the Vortex Viper line if I needed an inexpensive scope