US News and World Report ranks the top 20 rehabilitation hospitals like this:
1 Rehabilitation Institute of Chicago (Northwestern)
2 The Institute for Rehabilitation and Research, Houston (Baylor)
3 University of Washington Medical Center, Seattle
4 Kessler Institute for Rehabilitation, West Orange, N.J.
5 Mayo Clinic, Rochester, Minn.
6 Craig Hospital, Englewood, Colo.
7 New York University Medical Center
8 Ohio State University Medical Center, Columbus
9 Thomas Jefferson University Hospital, Philadelphia
10 Rancho Los Amigos Medical Center, Downey, Calif.
11 University of Michigan Medical Center, Ann Arbor
12 Spaulding Rehabilitation Hospital, Boston (Harvard)
13 National Rehabilitation Hospital, Washington, D.C.
14 Mount Sinai Medical Center, New York
15 Johns Hopkins Hospital, Baltimore
16 Albert Einstein Med. Center (Moss Rehab. Hosp.), Philadelphia
17 Stanford University Hospital, Stanford, Calif.
18 Shepherd Center, Atlanta
19 University Hospital, Denver
20 Hospital of the University of Pennsylvania, Philadelphia
That being said, I think that the list overstates some places and completely misses other programs considered in the field to be "very good." Virginia Common Wealth University in Richmond is an example of a good program that did not make the list. Some hospitals don't have residency programs (Craig in Denver).
I would be suspicious of godfather's advice. As someone in the field with significant research experience, I can tell you that rehab related research does make you very attractive to many programs and is sought after. Rehab is very multi-disciplinary and increasingly research oriented.
In general, you want to find a program that is gives broad exposure to all aspects of the field: Inpatient medical rehab, outpatient rehab, interventional physiatry, electrodiagnosis, pain, sports, occupational medicine, etc. I'm biased toward larger academic programs as they usually have the tertiary referral sources that makes rehab interesting. The trend is toward outpatient physical medicine training, but you can't ignore a solid inpatient training experience as this will always be PM&R's bread and butter: Stroke rehab, spinal cord injury, general orthopedic rehab, traumatic brain injury, degenerative neurological disease, and amputee.