Welcome to allnurses!
It seems as though your biggest concern with nursing is that the pre-requisites might not be challenging enough - everything else seems to point toward nursing. Well, except that you say some of the other pre-nursing students recommended medicine - was that because of how well you were doing in the science-based classes, or for another reason?
I have thought from time to time about becoming an MD (I've been a nurse for 15 years), primarily because I find it frustrating that some patients are treated in a way that I think is appropriate (usually elderly folk being overtreated even though they'll clearly not survive the admission). However I realise every time that this is because, however sympathetic the resident and registrar are, the consultant makes the big picture decisions, and I wouldn't be able to effect change on that level for decades, if at all.
You're right that there's more science in medical training, but peoples who are great in the sciences don't necessarily make good doctors. In fact there's a growing emphasis, at least in Australia, on medical school applicants to do well in humanitites, and there's more emphasis on interpersonal skills than ever before. One university that I know of (Monash) has dropped a year of science subjects as part of a recent curriculum reform.
Doctors do still get to interact with patients, particularly out of the hospital setting. They don't get the closer one-on-one, intimacy that nurses get, but it's not all Grand Rounds and scheduling tests. However, when I ask residents in medicine is what they thought it would be, they mostly say that they're disappointed.
Nurses not only get to implement therapy, we get to evaluate its' effectiveness; in ideal situations we also have input into treatment, but the flip side of this is that conditions are often not ideal, with some doctors seeing nurses as fuzzy-headed maids. This is fortunately an attitude that is dying off, but not fast enough
I quite like working with junior doctors - they're easier to mold! For the most part they start out overawed, as they realise they don't know nearly as much as they thought they did, and they listen to the nurses. Then, with a bit of experience, they start to get cocky, and ignore nursing suggestions. Ideally, this hubris is followed by a fall, which is when you can start having a more equal, professional relationship.
If you're still feeling conflicted, have you thought about shadowing a nurse and a doctor at a nearby hospital? While it won't give you a full picture, you'll probably get a clearer picture of what's involved. We often have potential nursing students spend a couple of days on the ward to get a feel for things.
Hope this helps - good luck!