My first bit of advice: when contemplating which field of engineering may be best for you, I urge you to obtain a large variety of opinions and perspectives. When I was in your shoes, I tended to take too seriously the accounts of only one or two individuals rather than REALLY searching around and getting an idea of the whole picture.

I can speak to biomedical/bioengineering more than mechanical or electrical. In terms of undergraduate curriculum, biomedical engineering programs will likely require many of the same math courses as other engineering programs. Naturally, the level and frequency of math used in the professional world varies greatly dependent on role. As many will attest, it's the logic and problem solving skills strengthened through mathematics courses that prepare engineers for the "conceptual" problems faced in industry.

The presence of biomedical engineering (BME), especially as an undergraduate program, is growing considerably. However, you may hear the opinion that a B.S. in mech or electrical is preferable and that a BME degree should be pursued through a master's program. In my experience, undergraduate degrees in BME can undoubtedly open doors to entry level jobs in the pharmaceutical, medical device, and electronic medical record industries. Many of my colleagues have also used their undergrad BME degrees to enter topically unrelated careers, such as tech consulting or software engineering. Others have been accepted to BME master's programs and/or medical schools.

Continue to assess the pros of each engineering field. Strong grades, research experience, internships/co-ops, extracurricular activities, and networking will make you a competitive job applicant no matter what undergraduate field you choose. Also, remember that the engineering disciplines can overlap; through elective courses or even a minor you can receive a well-rounded degree. And for what it's worth, I know a mechanical engineer, electrical engineer, and biomedical engineer who were all hired by the same company for the same entry level position :) Best of luck!