I think the main points have been addressed above. Note that the boundary between nurse and doctor is now blurring, with the emergence of nurse practitioners, nurses can train to be more diagnostic. Obviously you aren't going to be House or doing surgery, but if you want an opportunity to diagnose take note that it is open to nurses too.
I think at the most superficial level it is dependant on how much hands on care you want to give the patient. Your interest in the actual biology of disease would be a factor as well, as nurses do not need to learn this to the same level as doctors (from what my gf's Mum who is a nurse says, not dissing nurses).
The pay is obviously a factor, I know people who have been nursing for 30 years and haven't gone up much in the pay scale over the years. They still earn an okay salary (a bit below national average), but compared to some jobs the pay certainly isn't pitiful either. Doctors obviously earn a lot more (generally speaking). Yet again though, if you are a doctor who works in a hospice half the time voluntarily or a nursing manager that completely turns the table.
I don't know anything about you, but there is a slight elephant in the room: medicine is very, very competitive to get into. This might be something that you need to take into account, it is by no means impossible to get in, but it is a lot more difficult to get in. This might be something that you want to take into account. The other thing is, if you can't decide, write a medical personal statement and apply to both. I know of people who have applied to medicine with nursing as their firfth choice and there is no reason why you couldn't do this or apply to say 2 nursing and 3 medicines.