We have owned both Jayco and Keystone (currently Sprinter). To be honest, neither are 4 season tts. We camped in snow down to 20 degrees - our Jayco did not have heated (did have insulated) tanks and did okay as long as the fresh water was more than 1/2 full. The Sprinter (with heated tanks) had no problem. Both used a lot of propane to keep the tts at a livable temperature (65 degrees). We also have camped in both up to 100 degrees (115 in the Sprinter). Neither were able to keep the tt truly comfortable with 13.5K a/cs. In full sun, the best they could do was about 20 degrees less than outside air. The results were better in the shade.
Honestly, I thought the Jayco was a better made trailer. The Sprinter has a good chassis but some of the fit and finish is a little less than the Jayco. If we were just using the tts for an occasional weekend or vacation trip, no extreme temps or extreme backroads, either would be good. But for extended, extreme, or rough use, I would consider Northwoods products. In fact, we are getting ready to sell or trade in our Sprinter.