Pennk

I just did this yesterday actually.  School A accepted me with 3 years of funding, but only gave me 5 work days to accept or decline the offer.  As it was my only funded offer at the time, I accepted it within their timeline.  I had been accepted to School B and was in the process of interviewing for 1 year of funding.  After I decided that I could not say no to full funding, I contacted School B to regretfully decline, and they whipped up a full funding package that was more competitive than School A.  On a side note, all of my interactions with School B were so warm, welcoming, accommodating, and transparent whereas School A felt very cloistered to me. 
I accepted School B's offer and emailed School A to let them know that after careful consideration I would be accepting another offer.  An admin asked what school I would be attending (I did not answer) and my advisor wished me success in my career.  I wasn't happy to do it, but they seemed to not be terribly mystified that it happened.
Also, I have applied for even more competitive funding at School C (my dream location) and if that comes through, I may once again belatedly decline my offer to School B.  I don't feel particularly great about this strategy, but I feel like the whole process is just messed up with schools releasing acceptances and funding offers at such divergent points on the calendar.  This is my career, my future, and I don't feel like I am beholden to any University (besides the one I choose to attend).

I'm out at NYU (whatever the general public health thread was).  That's my application cycle done-zo!  I'm in at 3 out of the 8 schools I applied for.  One with guaranteed funding and two with funding I am waiting to hear back about!
1. U of Memphis - full funding for 3 years
2. U of Wisconsin-Milwaukee - interviewed for funding for first year
3. UT Health - I applied for a fellowship that would cover 4 years

I'm out at NYU (whatever the general public health thread was).  That's my application cycle done-zo!  I'm in at 3 out of the 8 schools I applied for.  One with guaranteed funding and two with funding I am waiting to hear back about!
1. U of Memphis - full funding for 3 years
2. U of Wisconsin-Milwaukee - interviewed for funding for first year
3. UT Health - I applied for a fellowship that would cover 4 years

That's so helpful, Pennk, thank you. In the end I decided against MPH@GW. And six minutes after I sent them my notice, I got an acceptance from another program I feel much better about. I'm not sure what that demonstrates -- perhaps just that today is my lucky day!

Re: Columbia SMS and maybe all doctoral stuff.  Emailed the Assistant Director of Admissions (she had previously emailed me months ago to clarify something on my app) last week for a status update.  She just got back to me and said that "doctoral decisions will be released shortly."  Hopefully that means this coming week.  I highly doubt I will be getting anything other than a rejection, but I would really like this admissions cycle to be over already!

Re: Columbia SMS and maybe all doctoral stuff.  Emailed the Assistant Director of Admissions (she had previously emailed me months ago to clarify something on my app) last week for a status update.  She just got back to me and said that "doctoral decisions will be released shortly."  Hopefully that means this coming week.  I highly doubt I will be getting anything other than a rejection, but I would really like this admissions cycle to be over already!

I did an online program (University of New England's MPH) but I am an employee of the University and got my degree for a severely reduced cost.  That being said, I would definitely not recommend UNE for anyone who wasn't getting a steep discount, but I cannot speak to any other program.  I will say that community building was extremely limited in my online MPH.  The most sense of community was in a Facebook group.  I do not know how GWU's courses are structured, but in my program each course had a course designer and several adjunct instructors who basically were graders. There was very little consistency across adjunct instructors.  Some were stellar, gave detailed, personalized feedback, and helped facilitate discussions.  Others were radio silent and basically just graded assignments (at one point I thought a professor had died or been arrested because he stopped grading assignments totally).  If there were discrepancies between the course syllabus and that week's module, often my instructor had to ask the course designer for clarification.  To me this speaks volumes about the fact that these courses were delivered by graders as opposed to instructors.  
I would really look into how courses are delivered.  Find the Facebook page and see what students are saying.  Ask to be connected with current students and instructors in the program.  See if you can find any accreditation documentation (not sure if these are made public).  Right as I was graduating, my program's accreditation totally went down the pooper and now they are in a process of amending some serious issues - lack of student governance being one of them.
I totally understand the merit of online programs.  I would not have gotten an MPH and be interviewing with PhD programs today without online graduate programs.  I think if you do some more background research and really look into what you are hoping to get out of the program - a degree vs. strong community, research options, networking options - you will be able to make a good decision for you.
P.S. I found it really difficult to get strong LORs from faculty in my program.  When I would ask for them the response was "I don't know if I know enough about you..." and I was like "I took two courses with you which is the most faculty consistency for me in this whole program!"  If there are a lot of adjunct faculty, expect a lot of one-off professors which once again limits your ability to make meaningful connections with faculty.