The Uni Kuru Toga is probably the best mechanical pencil (in my opinion), but that's driven in part because it's wonderfully engineered and I'm a dork for that.
I just got one. Digging it so far. My struggle has been to find a softer lead that isn't so brittle (I know this is like trying to find water that isn't wet). 4B is too soft. 2B is too hard. I wonder if a 3B exists...