Do the 1-year if you're pretty much all set with research experience and will be applying while you are starting MAMS. Otherwise, you'll have a year of nothing between finishing MAMS and medical school. The 2nd-year allows you to write a research thesis that goes towards your grades (which can be good), whereas the lit thesis at the end of year 1 is only pass-fail. Also, at the end of second semester, the last thing I wanted to do was write a huge paper.
Word of warning: work your damn tail off and find a good group to study with. Don't be a loner. If you study alone, you run the risk of being overly confident in the material. Studying with others in moderation will always help you judge what you know and don't know. It's also better to commiserate about things with someone's who's also going through this stuff. By the way, this WILL strain your relationship with your significant other.
Another word of warning: don't put too much faith in the professors. They are great people, but there are simply too many students to deal with. Although they will pump your head with good thoughts, they are ultimately doing that for everyone. A professor just can't be THAT committed to every student they talk to. They have a life and basically it comes down to the fact that no one has the coping skills to invest so much in so many others. You'll understand this 100x over when you become a doctor ;-) The better judge you are of how you are performing, the better you'll do in this program. Don't freak out when you realize how much of a cash-cow this program is for the university and that you will feel, at times, like you're just a number. You are, but just don't freak out about it... especially when you go to apply to schools. Also don't freak out when you realize that a lot of people get into medical school because they're really good on paper, but are otherwise awkward, clueless, or sometimes downright mean and awful people. They likely knew when to take advantage of things at the right times, which brings me to....
A third word of warning: don't be afraid to realize that you can be much more happier NOT going into medical school after this program. Hated the schedule you need to maintain to do well in this program? Don't trick yourself into thinking it'll change when you get into medical school. If you feel like you want out, don't waste your money applying to schools. Join the dark side (aka pharma or biotech). You'll make some money, travel, have hobbies, and won't grow to hate your significant other.
Realize that MAMS is a very expensive test of whether you're "right" for medical school. The last thing you want to think at the end of second semester is "I can't believe I wasted that opportunity!"
Best day EVER
