Both are extremely, extremely difficult disciplines and career options. They are also polar opposites. Medicine is all science. Being a doctor requires a lot of dedication, sensitivity, and a brilliant mind. Its long hours, and a lot of work.
As is law. My mother is a lawyer. Depending on how busy the law firm is, she can work up to 80 hours a week (which is normal for a lawyer). Not to mention that, yes, law school is very tedious and boring (unless its something you are very passionate about).
Not to sound like the responsible adult in the room, but seriously, the ideal situation in life is to find something you both love and are good at. Not a lot of people can achieve this- so if money is really your top priority in life, I would choose something that you are good at.
But remember, lawyers and doctors have insanely hectic and stressful schedules- they don't always have the chance to enjoy their wealth.
Also, if you really want to be a doctor you're going to have to realize that you are going to be constantly learning, constantly in that education process. Additionally, a lot of doctors don't finish their residencies/fellowships till after 28 or 29. Its just how the field works. Cardiologists typically serve anywhere from 7-12 years of residency and fellowships. Neurologists are a bit less, usually ranging from 4-8, depending on what type of neurology you would like to specialize in.
Well for starters, a neurologist, right now, makes about just under $200,000 dollars a year. A cardiologist has an average of about $305,000 a year. Of course it all depends on if you sub specialize, where you live, years of experience, private practice or public, how good you are etc. Don't let the internship and residency scare you too much because you will actually be practicing during these years, and of course, being paid. I am in a similar situation. I am a premed college student right now at Cornell and I am going for neurosurgery, which I won't finish with until I am at least 33, but I'lll have a first year wage of $350,000, and probably within 10 years be making close to a million a year. Medicine, I think, is long worth the wait.
The other thing about Medicine, is it is one of the few carriers where you can make really good money without screwing someone over, which you will probably find in law.
The thing about law is that you'lll make money if you are good, and if you are on the defense. The state or government isn't going to pay well.
That said, plan on either medicine or law, but most importantly, keep an open mind. Money doesn't always bring happiness. You have to do what you love to do.
PS the reason cardiologists make so much money is because there are a lot of patients out there with pulmonary disease, and often they do it to themselves. So as a cardio you will have a pretty tight schedule. There are not as many people with neurological disorders so that's why they make less. Neurosurgeons have less patients too, but they have the highest risk, and therefore the most training. Each specialty comes with its ups and downs.
Hope this helped. Good luck!