I went to the Syracuse and Carlisle shows, they're both worth seeing. Regarding which car to take, since there are a zillion cars at each show, I'd take the car that stands out most, so it doesn't get lost in the crowds of lines of similar cars.
The Dart draws a crowd with the ragtop and hot rodded multi-carb slant 6 for sure. I think the Valiant is better for a Mopar judged show but the Dart has that something different that draws a crowd.