I've been to every one on the list but SDC (granted some I've been to more recently than others). To put one as "the best" really depends on what you are looking for in a park (theming, dark rides, coasters, landscaping, layout, etc).
Dollywood is a REALLY well rounded park... fantastic on site resort, fantastic waterpark, REALLY good food and shows, nice themeing, great ride operations, and some of the nicest park employees you will ever meet. If you want that Disney "feeling", Dollywood comes really close (though not quite as well themed).
BGW is easily the most beautiful park in the US. The rides themselves aren't as well themed as I would like (though they used to have a few really good dark rides that they have since lost [R.I.P. DarKastle]), but they have a VERY solid collection of coasters. Not sure how I feel about the current direction of the park (Pantheon is great for a coaster, but the lack of themeing [and even lack of landscaping] concerns me for how future additions may impact look/feel of the park), but as the park currently stands, it is overall a great park,
Cedar Point is (and likely always will be) a coaster Mecca. And if you love rollercoasters, there is no other park in the world that you should be going to. The collection of coasters here is just superb (and it's not that they just have one or two good coasters and the rest are filler... Steel Vengence, Millennium Force, Maverick, Valraven, Raptor... all fantastic rides. Further, the on site resorts are all really nice. But if you are looking for themeing, or looking for family friendly rides, there are much better options.
Silver Dollar City is way up there in my "must visit" list... it's just so in the middle of no-where that it makes it hard for me to schedule a trip there.... hopefully soon... but from what I've seen, I could easily see why people love this park so much (especially given how many similarities it has to Dollywood, which I personally hold so dearly...)
Other nominations (though none that I would put as "the best" but some that could rank way up there) could include Hersheypark, Kings Island, Six Flags Great America, and/or any of the many smaller parks in the PA/NY area.