TimmyMax,
Basically, a DO is the same thing as an MD--you can write the same board exams (USMLE) as MD students do, as well as the one strictly for DO students (the COMLEX). This means you can enter an MD residency program, as well as look into DO residencies, all of which just helps to increase your options, as far as I'm concerned.
DOs end up working in private/group practice or hospitals, etc, along with MDs, in every specialty you can imagine. They get paid the same salaries, receive the same basic education, and have the same options open to them once they graduate. In fact, if you live in the States, chances are you may have even had a DO treat you at one point, without even being aware of it!
So what's the difference?
DOs learn a form of manual medicine, called Osteopathic Manipulative Medicine/Therapy (OMM or OMT), which ends up being kind of like an extra tool in your toolbox (as I've heard it described) with which to help diagnose and treat patients. It's really an incredible tool to use, especially when patients come to you with things like low back pain, and you have very few non-invasive options to offer them. Whether or not you choose to actually practice OMM once you graduate is entirely up to you, though--for some reason, the majority of DOs don't.
Traditionally, DOs have also had more of a presence in the primary care fields, and a lot of their programs stress this. In fact, I've heard KCOM is one of the best family medicine schools, MD or DO.
However, like I said, a lot of DOs don't choose this route, and end up in all kinds of specialties. Most DO schools have more than half of their students specialize in something.
The only reason I would advise not applying to DO schools is if you want to end up doing medical research (PhD)...most DO schools don't offer this option--in fact I think there are only 2 or 3 that offer a combined DO/PhD program.
But, if you're interested in becoming a really good physician (and I'm not implying that MDs aren't!) osteopathic med schools offer a great opportunity to do just that.
I hope that helps! If you have any more questions, feel free to ask! 🙂