I have only been to two of the Paramount parks, Kings Island and my home park Canada's Wonderland. Visually I think Wonderland wins hands down, I think a lot of planning lessons were learned from the earlier built Taft parks. The paving stones alone make for a much nicer environment. Wonderland is laid out very nicely and has some great sight lines.
I have been to King's Island twice, back in 1991 and again this year. I must say I like the mature sections of this park, although I don't like walking on asphalt. I don't like the way the Action Zone is laid out one bit, there is way too much concrete, and the rides seemingly plopped down with no regard to how they look on the ground. Son of Beast seems to have it's back turned away from the park. Top Gun is placed at the end of a long weird concrete path.
Although I have never heard this as being fact. I always figured Wonderland always suffered in the coaster department due to the lower value of the Canadian Dollar. At some points in the past decade our dollar was worth $0.65 US, that exchange can really add up when talking about a multi-million dollar B&M or Intamin coaster.