My goal is to go to medical school while working a good paying job after earning my undergraduate degree. Which do you think will get me into medical school the quickest and the smoothest? Which one of the majors has the best job placement right after earning your bachelors degree? My major is in biomedical engineering right now but I have heard it is EXTREMELY difficult and not worth trashing my GPA over; however, if it increases my chances in succeeding, i’m up for the challenge. Thanks!! 
You can’t work while going to med school. You have to get a job or go to Med school. You can’t do both. It might make sense to major in something that pays well in case you don’t get into med school, but don’t think you can work an engineering job and go to med school at the same time. That won’t work.
Also, you can major in anything to go to med school. It doesnt have to be related to biology. You can major in English and go to med school. The med schools don’t care what you major in.
Edited to add that there are standard pre-med courses that you must take but it’s not hard for most people to fit them in on top of their major courses.
For medical school rejects (i.e. most premeds), biology does not have good major-specific job prospects at the BA/BS level, due to the large number of medical school rejects in biology (about half of medical school applicants are biology majors). If you major in biology and do not get into medical school, be prepared to seek non-major-specific jobs (like many humanities and social studies majors do) as well as biology-specific jobs.
Biomedical engineering may be better but still not great at the BS level.
You do not have to major in any of these subjects to take the premed courses and apply to medical school.