I graduated with a degree in physci very recently, I'm a big proponent of staying AWAY from the major if you love your GPA dearly. That's what the game is all about nowadays. I only say this because the 3 PS111 (now 2) core classes are 6 units a piece! (WHAT?)
Once you know your grade in 111A, you are almost guaranteed to get that same grade in B/C because you see the same classmates (~250 students.... a majority of them with medical school aspirations)
What you learn in 2 years in undergrad will be covered in a matter of months in med school, so whether it gives you a leg up on everyone else is debatable. Just pick a major you love, but can earn a GPA you don't have to fret about when application season comes.(psychobio/biology/MCDB FTW!)