I've got a VX3 and a Nikon Monarch. To me, the monarch is better optically. It's pretty easy for me to see but it could just be my eyes. The VX3 is a 1.5-5x20 and the Monarch is a 4x40. It doesn't matter what power the Leupold is on, the Monarch looks brighter. That being said, I still think the Leupold is a great scope. I got it for the size, weight, and field of view advantage it had over the Nikon (...and I ran into a good deal on it...). I really like the thought of American made as well...
I've got a Monarch Gold, and it's definately a field above the Leupold, but it is price-wise as well.
Both have their advantages:
Nikon: brightness, lower price
Leupold: warranty, American made, size/weight, eye relief
Both have a lifetime warranty. There's others for each, but really it comes down to what you're looking for in a scope.
Take care,
JCM