Seriously,
Choose what makes you happy. Most students who do go DO as a "back up " find that their is no real difference in practice and are too busy slogging it out in residency to notice the difference.
Yep, they may be a tad bummed during that summer before matriculation because that they can't brag as much as their pre-med pals (if they are the bragging type). Yep, they may have to explain to Grandma Ethel, Aunt Mary and Uncle Chuck what a Do is 100 times. Yep, your arrogant cousin may get into Harvard Med and rub you nose in it. Yep, you might be shut out of some residency programs by misguided PDs.
If it REALLY matters, if those two letters (MD) REALLY matter to you more than the chance to practice medicine, go to an allopathic school. Life is too short to spend your whole career worrying over letters of the alphabet