I still vote for on-site. Recently, a very big perk called early entry was discontinued but I'm still hoping for a comeback on this perk. Another perk, e-nights are being reduced but they are still around. The environment and convenience are probably the best reasons to stay on-site. Also, they now have a character caravan to each resort on specified dates and times.
If you are without a car it's much less hassle on-site to get to the parks, etc. It's easier to take a mid-day rest. Resort Cast Members are more knowledgeable and helpful then the off-site resorts.
You have to be savy but you can get better rates if you watch for them for Disney resorts. There are no comparisons on the Deluxe end of resorts to nearby off-site resorts. The atmosphere is superb.
It does to a degree depend on how much time you spend at the resorts, too. Some people just may want a place to sleep and rather save a few bucks and there are more bargains to be found off-site. If you decide on off-site I lean towards the Downtown Disney resorts.
We've done both and it really depends on how long you stay, how much time you spend at the resort(swimming, dining, etc.), and your budget. When we visit Orlando, we have a tendency to make a long trip and we do many parks, not just Disney. It may be a good idea to do both on-site and off; so, you can experience the difference. One move is not too bad in a trip. This can be a good compromise.