The Schmidt is going to be the best optical performer out of the group and if you get the new model with DT II+ turrets you'll have some of the best turrets in the business. Mark 6 has had a shaky history, some good, some not so good, like 1911 above, the Mark 5 is the superior scope and I've had the 3.6-18 and while there were things to like, if you can afford the Schmidt it is the superior scope, but if you don't mind the reticles in the 3.6-18 Leupold I liked it more than the NX8. NX8 2.5-20 suffers from considerable edge distortion and finicky eyebox and parallax. I have a review of ultra shorts linked in my signature below, the ZCO, Schmidt, Kahles and now I'd enter the new March 4.5-28, I feel, reign as the best of the ultra shorts.