I really like my Nikon ED50 and the Promaster tripod and head I got from S&S archery. I find myself packing it when I'd leave heavier glass behind. I haven't seen the new Vortex 50mm yet but expect it would also be great. It is heavier than the Nikon by a good bit though and it will have to be really impressive to outperform the Nikon.
I've used my Nikon against my hunting partner's Vortex 85mm Razor and was really impressed with how close the little scope stayed. The Razor is better for sure, but not as much better as I thought it would be. The place we haven't compared them yet is at high altitude in really good clear air. At home and on our last antelope hunt the dust, mirage, and wind made the magnification advantage of the big scope play less of a role.
We bought our scopes to compliment each other and they do that well. We put in for tags together each year and mostly hunt together in the field.