Depends on the MD school and the DO school! Unlike what you hear on SDN, not all MD schools are created equal.
To make it simple with regards to opportunities: If you are accepted to a top 30-50 MD school, then you will have more opportunities. Otherwise a more established DO school will provide you with the same opportunities (if not more) as any run of the mill MD school! (I know this might be big news on SDN)! For instance, my DO school certainly provided me with advantages/opportunities over my state MD school (very average school) that I would've never dreamed about if I'd gone there.
But having said all of that, it sounds like you prefer the MD school; So please go there and let people who really want to be DOs take your spot!
While I agree that not all MD schools are created equal, your opportunities from pretty much any MD school will be better than pretty much any DO school. You should realize this since you are applying to IM, bala. For instance, look at IM at Hopkins, penn, MGH, The Brigham, UCSF, Duke, Columbia, and a whole host of other programs. No DO residents in medicine. Hell, Penn even has PCOM right down the street (and PCOM is considered one of the best DO schools) yet there are no PCOM or DO IM residents at Penn.
I went to a non-top 60 school and in my class alone we had a handfull of matches to Hopkins, matches to penn, multiple to Duke and UNC, MGH (urology even), Pitt, Michigan, Cornell, Columbia, UCLA, Emory, UVA, Stanford and the list goes on to the mediocre matches which most DO schools would consider to be excellent matches.
The major difference (and most impt thing), though is in the middle of the class. DO schools send their average students to medicre community programs while MD schools send their mediocre graduates to strong university programs. Very few are actually going to be at the top of their class, let's be honest. What a run of the mill MD school can do for the middle-of-the-road med students is much larger than what almost any DO school can do. This is not to insult the top DO schools but to highlight the reality- with the rare exception, MD schools are going to offer you more opportunites.