I have four Vortex Viper HSLRs, two older SFPs and two newer FFPs. All are 4-16x. None have given me mechanical problems, and the turrets track well. The only criticism I would offer is the markings on the parallax knobs are pretty useless (I don't find this to be a serious problem, I merely mention it to be fair). I prefer the newer FFP reticles hands down. At four power the thick bars that form the outside of the pattern provide plenty of guidance to the eye for a snapshot at close range, and at high mag the reticle center is an opening with a tiny (0.45moa) dot that has never posed a problem covering a target. I shoot targets at 1000-1100 yds, and find 16x adequate to the task for any size target I am likely to engage at that range. I don't think I'd like the 6-24x for hunting here in PA, as I am in woods with short sight lines and heavy cover quite often. Starting out with a fixed 4x as a kid, the 4x bottom end was a more practical choice in my mind. I have never had a chance to compare, but I suspect 4x has an edge at sunup and sundown too. I think I saw BDC turrets mentioned in this thread, I use Kenton Industries "Military" format, with both the yardage for my load and MOA scales to cover all occasions.