Both will be fairly high on my rank list.
K-Zoo: Pros: Strong didactics, very structured clinics, one of the best life-styles you will come across (home call five years), good variety of elective bread and butter ortho. Several fellows in every specialty exclusing tumor, although I am not sure about foot and ankle. Six months of the year, you will be in one of the nicest hospitals in the country. Outstanding benefits.
Cons: Only two residents per year means that you take a lot of home call over the years, a little light on trauma, a little too much clinic for my taste (I know I had the organization as a plus, but the volume is a minus) city isn't the greatest.
Grand Rapids: Pros: Great mix of tertiary care referral center and small private hospital, 40+ fellow trained guys in everthing but tumor, trauma up the wazoo, but nice life at the small community hospitals, huge volume or bread and butter ortho, great city for its size, probably the tightest group of residents I have seen on the trail. Not too much clinic you become an operating machine. Outstanding benefits.
Cons: Peds is up in the air right now. They have had an interim chair going on three years. Clinics are pretty crazy, you don't get much for continuity. You don't get to see a lot of scope work until you 4 or 5.
Head-to-head: I think Kzoo has a little better didactic program, definitely a better lifestyle, a better outpatient surgery experience, and a little more stable. Grand Rapids has a much higher volume, better trauma, a better city, and more in flux, both at the top and in their peds.
This is about as cerebral as I can be on this one. They are both strong programs, so I don't think you could go wrong with either. My list has been in for about 3 weeks and I just went with my post interview gut feeling, but that would have been my pro and con list had I tried to go that way.