Well, I do like Tolkien's own drawings of M-e. Other than him, I like some of Ted Naismith's(sp?) works -- he has very good clarity -- and a little of John Howe's paintings. I *despise* the Brothers Hildebrant's(sp) stuff in its entirety: I find it juvenille to the point of insult.
I have kept the version of paperback LotR that has Tolkien's drawings as cover art and box set art; I refuse to get another set (as the current one is looking a bit worn) until they go back to Tolkien's art (I really *am* a purist, after all) and *absolutely* refuse to buy any of the books that has *film* pictures on the cover -- bleh!
Tuor
I like what I've seen of Tolkien's own paintings well enough, but I do think that his skills at writing far surpass his painting skills. Which is to say that the above mentioned paint alot better than does Tolkien.