Busch/Sea World, with Cedar Fair a close second.
IMHO, the Busch parks have the best blend of high quality thrilling coasters along with absolutely gorgeous landscaping and some nice theming.
Disney and Universal are THEME parks. High on atmosphere, but too much is centered around putting you in front of a screen (looking at you, Disney Hollywood Studios and Universal Orlando).
Cedar Fair and Six Flags are AMUSEMENT parks. Great coasters and rides, but the ambiance is sometimes lacking.
Busch Sea World parks are the best blends of the two.
I've been to dozens of parks and on over 400 coasters, and if I were to get a free vacation to any US park of my choice? Hands down pick would be Busch Ggardens Europe in Williamsburg, VA. Phenomenal coasters, beautiful theming for each "country", and overall just a wonderful place.
Later,
EV