Curious on the STT Pro's as well. They were my second choice. They were newer so I figured I'd wait for more reviews and miles driven before I jump in. I'd definitely stick with an A/T in PA if you are going to drive much on the roads during Winter, if not using a dedicated snow tire.
Here are the TR ratings for A/T:
https://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=ORAT
Here are the M/T ratings:
https://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=ORMT
I would compare all categories that matter to you and your usage scenarios.
I just put on new BFG KO2's not too long ago and I drove them in the rain quite a bit over the past week or so (for the first time). It hadn't rained in a while, so there was also a lot of oil on the roads during the first day of rain. Mine did great and they didn't slide around on me at all. That said, I don't have anything to compare them with, other than my older Cooper Discovery A/T (30's) they replaced. I'm running 32x11.5xR15 with 27 PSI. Love them so far. Curious, are your tires new or older? KO or KO2? What size/PSI are you running? Hopefully they don't go downhill quick with age!