Although I watched both, I think I preferred Dynasty. Part of it might have been that they more younger characters (Fallon, Jeff, Sammy Jo, etc). I stopped watching Dallas around the time Victoria Principal left, but Dynasty I stayed with until the end. I even watched the spinoff, the Colbys (although mainly for Emma Samms and Stephanie Beachum... two actresses that I adored in the 80s).
I did watch all the rest, although mostly for very shallow reasons. Falcon Crest I primarily watched because I had the hots for Billy Moses, although I loved Jane Wyman's Angela Channing. Knots Landing I mainly watched for the younger characters, some of whom I found tasty. Like I said, I wasn't looking for deep storylines there