Three good optics. In this case, I'd say the functional difference between the group would come down to a specific optic to optic variance. If the ones I've used, I thought the Nikon had the best glass, the Zeiss tint was different but equally clear, the Leupold was a close third in image quality. The build quality on them all was great. The Nikon turrets were in this case my favorite, though turret feel is individual and what I like May be too heavy or light for someone else. None of the turrets displayed much slack and I trust them all to function properly. The feel was simply a little better with the Nikon. When it comes to using the scope, I'd say I was more pleased with the Conquest and VX3 than the Monarch. The Monarch is a little picky on eye placement. Warranty clearly goes to Leupold and Zeiss.
For me, if they all were the same price, I'd grab a Zeiss or Leupold, depending which coatings I liked the look of better. All three are so functionally close to each other that I'd buy based on warranty. It really is the separating factor. If price was different, and the Nikon came in at 65-75% the cost of the other two, I'd buy it. I think long term, if say I needed three scopes, that buying three of the Monarchs and having enough left over to buy a 4th should something go wrong would be a better value than having three Zeiss or Leupold optics and spending an extra $300-$400. Nikon is ok with their warranty, they simply require you to keep the receipt, which I never am good at. Still, with the number of problems I've had with all three (zero, knock on wood) I think saving the cash on multiple optics may be a better value. If you plan on handing it down, I'd grab the Leupold simply because of the image, the American heritage, and the idea that should something go wrong 40 years down the road, I have faith that Leupold would make it right to the best of their abilities and that they will still be in the riflescope market.
