from ohio, so i know these well; interviewed at both, but ranked them low cause I'm gettin out of ohio. otherwise, i would have ranked them both very very high.
CASE: excellent program; very friendly. Housestaff had the highest sense of comaraderie and friendship of any program I went to. The program director was a great person; you can tell he cares about the residents and works hard to ensure they are happy. Quality of education seems excellent. They have a lot of cardiology faculty moving there from Harvard. Research opportunities abound; fellowships are very very strong. Also, a lot of NIH funding.
OSU: partially biased toward OSU since its my college alma mater. They have an interesting program now, where every 3rd month is an outpatient month (it's part of the EIP - educational innovations project, that they are working on). They just named a new program director, who I interviewed with, who really seems to be a great person. Plenty of research opportunities, especially if you have an interest in heme/onc, with the James Cancer center at OSU, you would be well suited there. Fellowships were good.
If you are interested in heme/onc, you're going to be looking at large academic centers where there are research opportunities and good fellowship placements. Either of these would be more than sufficient to help you with your career plans. You should consider doing an away rotation at either or both of them as a 4th year.
Feel free to PM me if you have any other questions...