KI is the only one I went to when it was a Paramount park. Under CF I've been to all of them except CGA.
1. KI- The best overall collection of coasters, themeing, and rides. Even though it was the Paramount flagship, I feel the park has improved even more under CF.
2. KD- I have seen KD described as KI with different toys in the toy box. The similarities are crazy. Their IS is a little shorter but feels very similar. Obviously there are the clones (FOF, BLSC), the similar coasters (Racer 75 and Anaconda). Avalanche and Dominator are both really fun coasters and Twisted Timbers is great. I am not as big of an I305 fan as others but it is worth going there for. I like how the park has done a good job maintaining shade throughout the park.
2. Wonderland- There is a lot of charm to CW. Certainly it is one of the most improved parks of the last 10 years. I love Leviathan and Behemoth is great too. Their flats selection is probably the best in the CF chain. Sledgehammer is probably my favorite flat. The drawback is their coaster collection after the top 3 tails off quickly and their operations on the non B&M coasters could be better. There is nice shade and landscaping throughout the park.
4. Carowinds- Fury is my #1 Steel. Afterburn is my #2 B&M invert. I like Intimidator and Copperhead was a great addition to the park. Our old set of Flyers is the best flat in the park. You can tell KECO didn't design the park because it doesn't feel like KI, KD, and Wonderland. It really feels more like Cedar Point South with little shade and plenty of concrete. After the top four coasters the quality falls off quickly. Another greatly improved park over the last 10 years.
Depending on the day, I could easily switch the order of 2-4 but all are great parks.