I have the S-Tac 2.5-17.5 and a FFP SS 3-15. The S-Tac I have has great glass, tracks well and is very solid (not as good of resolution as the SIII). The S-Tac has a HUGE bell on it and I wouldn't put it on a hunting rifle or a pack rifle. I have the S-Tac on a POF .308 and it works very well for that. The SS 3-15 I have on a Savage Bear Hunter in .300wsm; it is my hunting pack rifle. The SS is very good, tracks very well and is very durable. It is perfect for a hunting rifle. I am not disappointed in either scope and if I had a new scope to buy I'm not sure which one I'd pick. From what I hear the new S-Tac scopes (different power than what I have) don't have as good of glass. That being entered into the equation, I'd go for the SS.