I really don't know who my favourite tileset maker is, but I can name my favourite level makers.

Shadow is capable of making excellent levels, but a lot of his more recent works which I have seen (Future of Evolution) aren't nearly as good as some of his older stuff like Slab Ratz or Darker Science, two of my all-time favourite levels.

Then there is CelL who is able to make outstanding CTF levels at very fast rates. Most of his levels are original and well-designed, especially his newest stuff.

BlurredD is definately my favourite level maker, though. His levels always seem to have something really unique in them (just wait until you see his single player demo), and I have yet to dislike one of them, regardless of the gametype.