Hi there,
People can be very passionate about the onsite vs offsite question...
We have done both and - at this point in my life - I'd say:
offsite for a trip longer than 4 days
onsite for a shorter trip
We are a family of five and although our little one is young enough that we could get a regular room, it would be too much. We stayed at AS Sports in 2011 and it was a basic motel room. The ME was nice and I found the bus transportation only okay. I did like the boat transportation from the WL though
For less than $100 night, I have found great offsite properties that are Disney-decorated and that offer 2+ bedrooms, a full kitchen, washer/dryer, multiple TVs and private pools. Like a PP said, I don't think it has ever taken more than 15-20 minutes to get to the parks. Our preference is to have our own car just so that we can come and go as we please and have the space of our own personal minivan.
It's a totally personal choice and I get both sides. We had a wonderful onsite trip in 2010 at the WL and had a super time. It was a short trip and at the time we just had two little ones. We got a 1-bedroom and that was perfect for 4 days. We felt the total Disney experience, but we paid through the nose!!!
The value rooms are (as another PP pointed out) basic motel rooms with two beds, bathroom and standard furnishings. The decor is exciting for kids and my kids really enjoyed AS Sports, but I found the food courts very expensive and not as varied as the options near the off site places we have stayed.
In a perfect world filled with golden coins, I probably would stay on-site at a 2-bedroom villa at WL or BLT so that I would have access to either the monorail or the boat. But, I'd have my own car so that I could venture off site when I wanted to for food/treats, etc.
Best of luck with your choice...you really can't make a bad one. Both onsite and offsite accomodations are viable options and have thier own set of pros and cons. Only you can decide what is best for your particular situation.
Space and cost are the deciding factor for us at this time, so off-site would be my vote. If the disney environment, EMH, and not having to rent a car are more important, than on-site is probably a better choice for you.
Remember you are at the happiest place on earth...so it's ALL good
