I would have to say that it depends on the roommate's personality than the roommate's profession. I just finished my M1 year and and during that time roomed with both. I started off living with a buddy of mine from high school who now works doing finance stuff. We moved after first semester because we had issues with our apartment being flooded with sewage and our landlord refusing to replace the carpet (by the way, anybody going to Missouri - looking for housing somewhere besides Deer Valley Apts!). Anyway, when we moved, one of my classmates had just broken up with his girlfriend and needed a place to stay, so we picked up a 3 bedroom apartment.
My med school roommate is actually somewhat louder than my professional roommate. We have different study habits and locations (I study at home, he hits the library). I thought that his moving in would motivate me to study more, but it actually just makes me feel guilty when I'm not studying, which doesn't help anything. I'm not saying he's a bad roommate or anything like that, just that you should not expect a med-school roommate to be an automatic study-buddy and empathetic companion.
My professional roommate is very respectful of our need to study, especially around finals. He is very supportive of us when we need to work. He knows enough about medicine (was premed) to take an interest in our stuff, but is disconnected enough that he provides a break from med stuff. This is actually tremendously beneficial. He is also relatively quiet. Despite my endorsement of a non-med roommate, I cannot emphasize enough how bad it would be to have a roommate that isn't considerate of your needs.
Having been in your shoes just a year ago, I know that med school can seem like a huge, daunting challenge that is going to consume your whole life. If you let it it will. Having a roommate that isn't in med school, however, can provide an extremely beneficial break. Think about it. All day at school, you are going to be around med students. Do you really want that when you home at night? Having a fresh face that I can crash and watch TV, talk, whatever with is awesome. I feel that I probably do better in school by not stressing as much because I have someone else I can do stuff with. If you have other friends at the school you will be attending you can hang out with, great, maybe a med school roommate would be good for you. If, however, you aren't going to know a lot of people outside your class, having at least one that you live with will help a lot.
