All the Vipers are popular, mainly because they have desirable features and acceptable optical performance for their price point. The optical contrast is marginal, however, because of higher than average veiling glare. That is my personal assessment from having evaluated them several times at the last three SHOT Shows.
My recommendation depends on your application. For target shooting, and predator and PD hunting I think Vipers are great. For big game hunting, however, I recommend looking elsewhere for scopes that have better glare performance.
What is your application and budget? The more info you provide on caliber, range, reticle preferences, etc., the better the advice you'll get on this board.