I have the S1 3-9x40 mildot and I have had very good luck with it so far. Sightron is an excellent value for what it cost. Aparently the difference is the ED glass and the coatings so better glass = more money. The S1 will do the job though.
"New for 2007, the features found in these scopes are unsurpassed. The Enhanced Definition glass ensures the highest edge-to-edge fine contrast and resolution available. The Sightron Big Sky line includes Sightron's new Climate Control Coating on external glass surfaces and are enhanced by their 7-layer Zact-7 Revcoat multi-coating on all internal surfaces make these optimal for any and all weather and light conditions. New Finger Adjustable Windage & Elevatiuon controls that are resettable to zero will be found on all Hunting models. Newly designed Adjustable Objectives that are good from 10 yards to infinity and a constant long eye relief with a minimum of 3.8 inches on every model. All scopes will accept sun shades and indeed stackable for individual requirements. Durability ensured with their true monotube design. All Sightron SII Big Sky scopes feature Sightron's newly improved ExacTack system for unsurpassed repeatability and reliability."