Well, I like Insane Steve's levels; for me they're the best of all.
I don't really care about design, I like the straight terrain and love the neat puzzles and the trickiness in the levels.
Since they are usually small they are quite nice to play, having a first look at them most of them look interesting at once, and usually they are also interesting to play.
Of course there are also some not so good levels, but those appear not so often at all.
Since I don't care about design so much, Hubbart's levels should be not really special to me, but some of the are quite impressing though.
(Oops...seems that it's getting a little off topic...)