I've had both and the Sniper suits me better (I've also had the Bushnell 3200 too and like that too). I liked the MTC reticle but in the end the optics of the Sniper make it a better bet.
Given that maximum parallax error is a function of the size of the objective, the EB Sniper's 42mm objective should theoretically produce less maximum parallax error than the Viper's 44mm objective. In practice I'm not sure. I think Tim Finley's articles showed less error for the EB Sniper but I might be wrong.
As Ryan said though, ultimately the setup of your cheekpiece/stock/scope is probably going to be critical in helping you to get a consistent head position behind the scope.