Personally, I'd go with either the Black Diamond 4-16X50 or the VX-III 4.5-14X50 because both have side focus and a range compensating reticle. The 4200 is a great scope, just not available with many options, and in a scope for PDs, I want SF and a mil-dot or other range compensating reticle, 'cause I hate turning knobs to compensate for long range shots. In the 4200 line, the 6-24X40 version is available with SF and MD reticle. Since you said you'd be using it for PDs, I love the Leupold Varmint Hunters reticle for this application. It features wind compensating dots and a handy "prairie dog gauge" that really helps with rough distance judging. In addition, it is a very fine, glass-etched reticle. I've made many long range shots using this reticle. I disagree with the statement that the others would be a "better scope," as I've found the new VX-IIIs to be comparable with the 4200, Monarchs and Black Diamonds, having owned all of those. While I do agree the Leupold is a bit overpriced compared to equal or better competitive scopes, one thing Leupold does offer is options, and this is one of those applications where I think the VX-III really makes sense. I do a LOT of PD shooting, and I've used all these scopes in field conditions in the worst sort of mid-day mirage, and I think the new VX-III's optics are getting a bad rap based on the old VARI-X IIIs. I also consider a range compensating a near must for this type of shooting.
Edited by RifleDude