I have looked through all three over the last couple of years, the night force is very clear but the difficulty in re parallaxing the scope is a turn off. The viper I thought was no where near as good as a little Leupold or the night force clarity wise. The picture seemed far more dull and the scope is phillipines made I recall. I could be wrong. The Leupold is clear and easy to adjust, the TMR reticle is superb. Not too thick which I personally like.
You can never shoot enough pellets