The viper is better, if you get the upgrade suspention, they had it at the dealers for the first couple years. the viper s had the upgrade already in it. there nice trail sleds. i wouldnt go as far as more reliable, then a four stroke, well at first my vector had a reverse jit but in it, when my mom owned it, and the messed up the chain case gasket, so up in canada for a trip she leaked the hole way, but not yamahas mistake. now i bought the vector from her and she bought my step dads viper and he bought enougher viper. when she had the vector she rode the viper. she sayed she didnt like the way it rode, comparison to the viper. Her viper blow a crank this winter with well over 8000 miles on it. the sled when we bought it had 2000 but the guy never broke 60, blow a piston that year, when my step dad owned it. the sled wasnt used to running 90 on a trail. and the new viper is in very nice condition, only 1500 miles and its a viper s. the owner was from are small town and we knew him, and how he rode. the red viper (my moms has the upgrade suspention) same as the newer one. the red viper has a new enigine now, and is ready for this year!!!!!! there really good trail sleds and with are 2 vipers and a vector i think we have the best trail sleds for how hard we ride on trails