I am a MD. My wife is a DO. I graduated med school in 2006.
From a knowledge perspective, MD and DO schools teach basically the same breadth of information. MD schools are more competitive to get into and DOs schools tend to be less so (and are still probably back-up schools for people who can’t or didn’t get into a MD school).
Really, the big difference is that DOs learn osteopathic manipulation, which based on my limited exposure is part legitimate and part quackery (a little to chiropractor-ish in my opinion). Most DOs out in the real world don’t seem to practice it, though, and most practice medicine in a very similar fashion to a MD. Nowadays, in my experience, there’s really not much difference between how a MD and how a DO practices medicine.
I think the lines between the two will become even more blurred as the residency matches for the two merge into one one (i.e. may see more and more DOs doing their residency in MD residency programs).
I know a bunch of worthless MDs and a bunch of really sharp DOs (and vice versa). Ultimately, it’s a personal choice and you should choose someone who you feel has your best interest in mind, regardless of title.