Take upper division biology electives if at all possible. I decided to take immunology, medical microbiology and molecular biology as electives my senior year and LITERALLY the first THREE passages on my MCAT BS section went; immunology, medical microbiology, molecular biology. It was a hugh confidence booster and allowed me to finish the BS section with 20 minutes to spare.
Granted, the questions weren't word-for-word from my classes, but it was incredibly helpful that I had to spend ZERO time "getting my bearings", so to speak. If you've seen the concepts before, that's about 80% of the passage right there. You definitely do NOT want to try to be learning things like Real-Time PCR or B-Cell affinity maturation on-the-fly. By learning a lot of those concepts beforehand, you will save yourself a lot of valuable time. That time can then be focused on understanding the 20% of the passage that is new information that the questions will likely be asking about.
The moral of the story: Take advanced biology electives. There's a much better chance they'll be useful on the MCAT and will make medical school a little bit easier for you. Plus, nobody on an AdCom is going to be impressed by 12 credits of 'A' in "Interpretive Dance" or "Intro to Art" classes. Furthermore, if your Philosophy teacher turns out to be a total schmuck and you end up getting a B in Philosophy ... eye-brows will be raised.
Good luck man!