I think the Viper is generally the more popular model because of....

a) Most folks like the sit down/stand up feature of the "Barred climbers".

b) That level, front bar adds an extra feeling of safety and security.

c) Most deer hunters are either bowhunters/riflehunters or just riflehunters and that level bar provides excellent support when aiming a rifle.

Either stand would be a good choice but I personally prefer the "open-front" models for bowhunting as I believe they allow a slightly greater freedom of movement.