I have the ED2, but have never laid hands on a Nikon other than the ED50. Not sure what size Nikon you are referring to but I'm guessing the midsize given the price. I have tested my ED2 side by side with a Swaro STM 65 non ED. To myself and my bud who owned the Swaro, the ED2 was better. Not by much though, and it could have been attributed to the larger diametere lens. The ED2 did make better use of the higher magnification levels, 45 or so and up.
The ED2 is a very good optic that, for the price, especially today's price, is a great value. Personally I much prefer the 2 stage focus knob to a single stage. Being able to fine tune the focus is a huge benefit. The camera adapters for the Vortex will fit the ED2. I have taken some really nice photos using my Canon SLR and the ED2.
I have had to utilize the warranty after dropping mine on asphalt. The two halves of the body came apart at the rotation ring, not completely, but it was no longer sealed. While Zen Ray did fix it, I was without a scope for a little over 3 months. From what I hear vortex customer service is much faster so that may be a consideration for you.