Doctors diagnose and treat
Nurses promote health
The roles are both caring for patients but from a different point of view, philosophy and focus. If you want to be the one to diagnose and come up with a plan of care for a patient but you don't want to be the person actually delivering the care then medicine is better for you. Nurse don't actively diagnose (though we do all the time) but instead, figure out how to to get the person back to their optimum health and spend their entire shift with patient. The doctors do rounds, see the patient for 10-15 min then leave and move on to another patient.
For example, a doctor writes in the post op orders of give pain medication as needed not more than every 4 hrs and to get the patient up out of bed at least 2x/shift. The doctor has no knowledge of how exactly the nurse will accomplish this.
The nurse determines what time to give the pain medication and times the pain medication for about 20-30 min before he/she plans to get the patient out of bed. The nurse is an expert on how to turn the patient, drop their legs of the bed while sitting them up in a single motion. The nurse knows how long to let the patient sit before standing or even if the patient appears able to stand. The nurse determines how long the walk will be and figures out how to get the person back in the bed.
So you have to look at the two roles to determine what fits you best.
I hope this helps!
Best of luck!