I have never even looked through a vortex so I have no opinion on them. But I own many Leupolds & several Nikons. I will take the Leupold VX-II or Vari-x & VX-IIIs (3-9's, 4-12s, 1.5-5s, 2,5-8s)over my nikon Monarchs(2-7s, 3-9s). But I like the Monarch better than the cheaper Leupolds.
The biggest thing I disslike about Nikons is that the "sweet spot" to see through the scope is very small. If you are not right on then it is like looking through a stovepipe. Leupolds are much more forgiving in this respect. IMHO Leupolds are just plain better hunting scopes.