Okay, clinics vs hospitals...

Medical Clinic - $400 to build - $400/mo ($100 ambulance) - 500 patients (550 if funded to $460)
Large Medical Center - $1100 to build - $1200/mo ($200 ambulance) - 3000 patients (3300 if funded to $1400)

Ambulance costs allow you to change the service territory of your medical facility. So, for instance, if you have an over-loaded medical facility in an area with overlapping coverage from other facilities, you can just cut back on Local Ambulance Funding and lower the number of patients being brought to that particular facility.

Costs per patient:

Medical Clinic - $0.80/patient at full capacity. $0.84/patient at 110% capacity
Large Medical Center - $0.40/patient at full capacity. $0.42/patient at 110% capacity.

Common sense dictates that you should always place the large medical centers... unless I'm missing something.