It seems like a lot of good responses here. I'll add one more. In my army days, I was the squad designated marksman, I had an M14 EBR with Leupold 3.5-10x40 second focal plane, and I had the opportunity to change the optic to a Leupold Mark series with the first focal plane. What I noticed immediately is being able to range at any magnification. See, with the second focal plane, you generally have to range at 10X to find the proper distance of a known object (using the height of a person, for example). With a first focal plane, because the reticle is etched on the first plane, the magnification of the reticle and object in site scale together, which means you can range your target at any magnification. As the magnification is increased, the reticle grows with the object. So if you need to magnify to say 18X, you can take an accurate range estimation at the magnification instead of having to dial the magnification down the 10X to do the math for range estimation with the second focal plane setup. I will say that the reticle on a first focal plane at low magnification can be difficult to use, but it shines above 10X when you don't need to change magnification to range estimate. In my personal opinion, it comes down to application. I found a first focal plane to be quicker than second when it comes to range estimation. If you are shooting known distances, you know your holds, generally shoot at the same magnification and don't want to move clicks for pellet drop/wind than I would stick with a second focal plane. At the very minimum, make sure you get a scope that is either mil to mil or moa to moa. Don't mix and match these two scales. If you ever decide to dope your scope on the fly, you are going to punish yourself with math.