I'm looking into going back for my PhD. I know for me, I NEED to do it the old fashion way. I tried one semester of online for my MSN. it was 10 years ago, I and a small child at the time and I worked nights. I had no ability to structure and discipline myself. I transferred to a brick and mortar school. I needed to be AT school, not in the house "at school". I also didn't like that I did not know my classmates (I don't think that would bother me as much now, because I have become much more social online).
I also have the ability to do it fairly close to home, and it works for my schedule. One day a week, all day. It is part of the university system that I work for, they will pay for a good part of it, and my boss will give me that day off, and rearrange my schedule accordingly.
It all depends on your situation, what's alternatives are available to you (brick and mortar in your neighborhood), cost, and resources. Some of my colleagues enjoy the fact that they can do their work at 3am on their couch. I am not productive at that hour, so that's not an advantage. I don't have child care needs (a 13 year old who gets herself to and from school). I have the ability to make it work with my schedule. And I feel much more motivated when in a traditional classroom.
Also, be sure to look at any on-campus commitments the program may require, and where they are. It may only be once a year, but if its in a location that will be costly for you to travel to (or you hav e commitments you cannot get out of at home), this may be a deal breaker. My online MS program had an on-campus orientation, 2 or 3 days. It was about an hour from my home, so it was doable.