I had to go with The Shawshank Redemption. Not only is it the best movie of the lot, but it's the one I've revisited the most.
My second favorite would be Kubrick's version of The Shining followed closely by Carrie.
Making a top ten list of King adaptations would be tough. Many of them are almost equal. Others I really like (in no particular order): Stand By Me, The Green Mile, Creepshow and The Dead Zone.
The solid ones: the original Salem's Lot, Misery, Christine, Silver Bullet (Busey + werewolf = cool), Pet Sematary, Apt Pupil, It (dumb at parts, but I'm nostalgic for this one) and Storm of the Century.
The mediocre ones: Cujo, Cat's Eye, Maximum Overdrive (okay, it's bad - fun schlock, though), The Running Man, Rose Red, The Dark Half, Riding the Bullet and The Shining mini-series.
The bad ones: Thinner, Children of the Corn (sorry, don't like it), Graveyard Shift, Sometimes They Come Back, Sleepwalkers, The Lawnmower Man and The Mangler (it gets point for having Robert Englund in it, though).
I haven't seen the rest, and that ashamedly includes The Mist.
Did anyone here see Hearts in Atlantis? I really want to see that one.