I have both, the Sightron SII36X42BRD is on a CZ452 for Rimfire score shooting and the Weaver 36X40AO is on the Viper. Of these two particular specimens I like the Weaver better. It seems a little brighter, a little clearer and the clicks are more positive although I have never handled the Sightron Big Sky model. The SII has the price point advantage of costing about 2/3rds of the Weaver and there might still be a mail in rebate of $50 to $75 depending on which model Sightron you buy. On pages 34 and 35 of Mike Ratigan’s book Extreme Rifle Accuracy copyright 2007 he speaks fondly of the Sightron which I believe is the SII model because I don’t think the Big Sky was around in 2007. On the 6mmbr website they did a comparison of target scopes
http://www.6mmbr.com/optics.html and rated the Sightron as “best buy”. Although I prefer the Weaver, if something happened to it, I would put the Sightron on and shoot. If money were no object, I am lusting after a Leupold 45X but get the best you can afford and shoot.
Dwayne