For anyone under the age of 21, Children's Hospital is one of the best in the city. Otherwise, I recommend Christ or University. Honestly, Cincinnati has so many good hospitals to choose from that it really depends on your needs and location.
There's an old Cincy joke about hospitals. If you're really, really sick, go to University Hospital. They're a teaching hospital with some of the best doctors, experimental procedures and latest technology. The other part of the saying is: If you're not really, really sick, go someplace else.