Neuronix is right in that it is very difficult to compare programs like this. More specific questions may be more helpful. I am a graduate of the Case MSTP, so I am very familiar with that program. I assume by MSSM you mean Mt. Sinai in NYC, but I'm not even sure.
Case is a strong and fairly large program (12/year). The strengths of the case med school are innovative curriculum, pass/fail grading for first 2 years (which cannot be overestimated!). The MSTP has an outstanding director (Dr. Harding) who is an outstanding student advocate, and the program is very responsive to student concerns and does everything in its power to address any problems. That being said, most programs are like that.
Strength of the Case program are close ties with Cleveland Clinic Foundation, which opens like a bazillion other research labs, tons of good hospitals you rotate at in M3-M4, etc. Strengths in research include neurosciences and biomedical engineering. The tie in between BME and the medical school is probably as good as any in the country, and every year 3-4 people get MD/PhDs through the BME department.
Weaknesses are probably location, depending on your perspective. The weather is terrible and the cleveland economy is in the dumps. On the other hand, your MSTP stipend goes a long way and you can get a great place for a little money. This gets more important near the end of your 8 years when you're either living in a nice apartment with your wife or a cramped apartment with other medical students.
Of course, this commentary comes with the disclaimer that I was a Case MSTP graduate and I had an excellent experience there. Case has an excellent MSTP web site where you can get more information (
mstp.case.edu) As neuronix said though, there are no unbiased opinions. PM me if you have questions.