Personally, I both like and dislike TD's approach to Planescape. I do like his almost whimsical style, cartoonsih looking characters (which he can crank out in droves and still have them looking unique), but I really didn't like that particular atmosphere in my PS campaign itself. My and my old group were far more into gritty and dark atmospheric qualities. TD's architectural art was fantastic for that (just check the Factol's Manifesto for his take on the faction HQ's).
Brom did interior artwork for much of the original Dark Sun box set, in pencil sketchings and shadings. They were rushed and vague and actually did alot to make the setting stand out. I don't think that style would have worked for PS, even if he did some great paintings for Dark Sun. His cover work did sell me on Dark Sun, even if his iconic Conan style fighters got a little old. Anything he did without a 'massive hulking warrior' was just plain cool as heck, like the Veiled Alliance cover, or the belgio on a cliff image from both Dragon mag 173 and the Dragon's Crown Adventure.
