maintaining a high GPA
preparing for MCAT
preparing for rigor of med
completion of pre-reqs
Others may disagree, but I can only based my opinion on D’s experience. She graduated from Med. School in May.
I do not think that major is important for the first 3 of the 4 above. Some major will require more efforts than others though. Specifically, engineering is the hardest of them all. But maintaining a 4.0 in engineering is still possible and some on CC are done it. Well, we are still talking about UG. Do your work in every class, do it on time, do it correctly and seek help when there is slightest doubt in understanding of the concept. These will lead to A in class. No genius is required, but, again, many here believe so.
You will have to prepare for the MCAT, no matter what is your major. One exception is if you are particularly very good at some subject(s). Again, D. mentioned that upper Bio classes (physiology, genetics, others) were very helpful. Do not get me wrong, she still took formal Kaplan class and was preparing for MCAT a lot outside of classes. She also said that scheduling the MCAT right after her junior spring finals (Physics, physiology) was helpful. Again, major does not matter. D. took the old MCAT, but maybe she would be better at new one, she took tons of psych classes for her neuroscience minor.
D. said that one cannot prepare in UG for the rigor of med. school. According to her, the academic level of classes in med. school is quantum leap higher than in UG. However, what has helped her is great time management skill that she has developed since age of 5. Being excessively busy with your life will help. She kept herself very very busy in UG, many ECs (all medical ECs were done during school year), job, 2 minors, even tried her sport in freshman year, had to drop it later. This enabled her to continue being involved with ECs even at Med. School and these helped later when she applied to residency. Anyway, keeping yourself busy at college is a good idea, again, major does not matter.
Yes, some majors will have all med. schools pre-reqs included. But, again, you should choose your combo of major (s) /minor(s) based on your interests. You do not want to put yourself thru 4 years of misery in UG, you want to have a satisfied life in college, otherwise, it simply will not work.
Best wishes!