I'll agree with kcald on this one: it's a matter of personal preference, knowing you learning style, and, of course, what is possible/feasible given one's personal situation. I chose an online programme because we ended up moving to a city a couple of months ago (and we are *not* moving again!) where there's only one school and I didn't get a good vibe from the department when I initially contacted them.
The online experience can be good: I'm taking a couple of pre-reqs this term and found a pal in each of them fairly early on (and one or two good classmates, wherever they are, is worth a lot to me). I've also had one fantastic learning experience, as the instructor is extremely good and highly responsive. The other experience is dismal, and although I don't think that is a result of the online nature I DO think its poor quality is facilitated and enhanced by the fact that the instructor is, well, distant.
One thing that necessarily occurs in online courses is the delay in feedback: one student asks a question, another student sees it the following day, the instructor responds 24 or 36 hours later, other students see the response. In a classroom setting, all of this happens in real time and everyone present is on the same page. That can be a nuisance, but in my opinion it's surmountable.
I also think that the experience in a cohort-based graduate programme, whether online or on-campus, is going to be much different than the experience of a few online courses outside of a degree programme. In one semester, there's simply not enough time to forge relationships and, as many of us know, there will always be students who are at different levels or who aren't as motivated.
In the end, it's a personal decision, but it's a good one for me!