Cooper makes good stuff, they also make lesser quality tires (as does BFG). In tire quality you want to consider rubber compound, tread design, shoulder reinforcement, sidewall design and reinforcement, load rating, temp rating, wear rating, speed rating, and terrain the tire was built for. I don't think anyone in this thread has mentioned a tire to be concerned about when looking for good to best quality.
IMO the BFG KO2 is as good as an A/T tire gets. The Cooper A/T tires are also good tires that offer good traction. You will probably trade some road noise for some off-road wet/mud traction looking at that STT vs. KO2. The KO2 by nature will give you a smoother and quieter ride where the STT has better tread spacing between the blocks (better cleaning when in mud/clay/soft dirt). Both tires will damage/puncture if you air them way down and abuse them. Both tires should perform just fine on the road (although I think the BFG has a better design for road manners).
If you are still looking at this option I would ask you what YOUR driving style is going to be like? I drive my rig on the street every single day and don't do a lot of mud wheeling so the BFG was a natural choice for me. If your rig is more of a weekend warrior and OFF ROAD WET traction is more important to you than I would change your options to Goodyear Duratrac vs. STT.
Yes, the KO2 is much better in wet conditions than the KO was but there are still better contenders in the A/T category. Your only other route is to abandon street performance and comfort for a true MUD tire.