With the excpetion of one program, the "best" neurosurgery programs tend to be at the places with the "best" other programs; but of course it depends on who you ask. Some of the programs considered the "top" would include
Barrow (in Phoenix - they do their stuff at St. Joseph's Hospital)
1. University of Washington
2. mgh=b&w - harvard
my list (based waht i heard from residents at columbia, harvard, and a couple of other schools).
a not-so-well-known program may have one attending that is a superstar, though.... you'd rather learn from him than from someone who got into neurosurg and then decided to concentrate on other hobbies.... wouldnt you?
program ranking is mainly based on research (basic and clinical) coming out of those departmetns. some medical schools may rank among the best, but may not have a very strong neurosurgery department.
(for those skeptical about b&w neurosurgery - until 3.5 years ago brigham and women's in boston was one of the WORST places to be (they had trouble finding residents). then dr. arc day joined them (was in florida before that) and look at the quality of their residents since....)