I was struggling with that same question when I made the choice to go into into respiratory therapy. Back then, the deciding factor was the amount of technical work that was involved. I was really taken with ventilators and still am, but I eventually made the jump into nursing because I was frustrated with the limited scope of respiratory care. I did everything, really that I was trained to do but wanted to do more patient care. I've been working as an ICU nurse for awhile and find that I'm doing both and feeling pretty satisfied. I still work with ventilators but now have added balloon pumps, hemodialyzers, PA lines, VADs and more. Eventually, I will go into advanced practice, maybe anesthesia which was my plan when I made the switch because it combines my favorite parts of both jobs. If not that, I might go into family practice because after many years of disease treatment, I find disease prevention very appealing.
If you haven't already done so, think about job shadowing nurses and respiratory therapists to see what the routine is and envision yourself doing those things. Check out different hospitals and nursing units and ask questions. While you're looking around, check out cardiovascular technnology. It's a technical job in a fast paced area and is a growing profession. Meanwhile, it may still be that both nursing and respiratory care are equally appealing for different reasons so you could end up starting where the first opening occurs. Don't feel stuck because you can do like like many people before you did and switch careers. There's a lot of common education and getting the other degree doesn't take very long.
Good luck,
R