Pyle is great.
I don't recall having read Knowles, so I can't compare.
Although not "traditional", Mary Stewart's Merlin trilogy is exceptionally good for a combination of both realism and mythic/magical elements.
Her stand-alone The Last Enchantment, told from the viewpoint of Mordred, is excellent. (Her take on Mordred departs greatly from Mallory, et al.)
For the closest thing to a "historical" Arthur, Rosemary Sutcliff's The Lantern Bearers and The Sword at Sunset are probably the best ever written. Sutcliff also has a traditional Arthurian fantasy trilogy, but I haven't read that (and really need to add it to my list).
White's The Once and Future King is its own thing. Marvelous, and built with the tradition as the skeleton, but fully a modern novel with modern sensibilities, language, humor, and points of view, philosophy and even politics. (Well, modern in 1930's England). I love the excerpted The Sword in the Stone more, but The Once and Future King is still high on my list.