The answer of which is best depends on which things you value.

Radiologists have the highest malpractice rates (its hard to prove an opinion was right when the evidence is on film). Radiologists rarely see patients unless there is a special procedure in the radiology department. With digital technology there is a possibility that radiologists can work from home for at least part of their week. Depending on the hospital and the contract, productivity expectations may be really high. You have to like doing the same thing day in and day out (think 200 mammograms, 400 chest xrays etc)

Oncologists see patients and can specialize in different areas (breast, GI, pediatrics etc). They see patients and can also practice surgery. There may be emotional stress as there are highs (saving someone) and lows (losing someone); it can be rewarding to take this journey with patients and make them healthy and/or comfortable. You would have to be ok with continual learning as new treatments constantly emerge.

If you like both specialties consider radiology oncology 🙂

http://www.radiologyinfo.org/en/careers/index.cfm?pg=rtcareer&bhcp=1

A radiologist is a doctor who specializes in the interpretation of xrays and other diagnostic imaging tests. An oncologist is a doctor who is board certified in the care and treatment of cancer patients. Both doctors work in hospitals. Both make a lot of money, but, judging from my latest bills, radiologists REALLY make a lot of money….from me, anyway. I would think being an oncologist would be a great deal more stressful. The positives, I think, would be hard to find in that discipline. The negatives would be the fact that many of your patients are going to die no matter what you do. Add to that the emergency admissions of your patients to the hospital and you get called. They start vomiting in the middle of the night, and you get called. You have to be available 24/7 or have someone taking call for you. I would choose radiology. Seldom any direct patient contact, just read the tests and report to their doctor, or the ER doctor. The negatives would be that you would rotate through call at the hospital, but that is with almost every patient care job in a hospital.

If you are looking for a job that is not too stressful for YOU, medicine is the wrong career choice because the patient is always first. If your attitude is “which is least stressful” rather than “where am I suited to do the most good” get a career doing something else. There are already too many callous healthcare professionals.