We've done both.
A few years back, I would have said offsite.
Now it's onsite.
The cost difference isn't that much, even through Skyauction. Once gas and parking costs are figured into the equation, it's a wash. The time factor weighs toward onsite.
Like the dining choices onsite. The food courts are great, there's something to feed everyone in the group. Eating offsite adds time and we end up eating at places we eat at home anyway, it may be a few bucks cheaper, but not enough to matter. I am not cooking on vacation.
With a suitcase full of shorts and tshirts, doing laundry at Disney is $8, that is nothing in a $2,000+ vacation budget.
Like Disney's pool hours, if I want a swim after a day ends early at the parks, I can head out at 9-10:00 and do that. We've stayed at the Fountains and Silver Lake, those pools close at 10:00.
As for TV's, we can do that at home. After a long day at the parks, the TV never usually even gets turned on. If I want to watch a sporting event, there are places onsite to do that.
Basically we found that the luxuries of staying offsite are just not worth the time as staying onsite. The onsite stay is very convenient, with everything within the resort boundaries, a 3-5 minute walk to the bus, food and swimming is within a few steps, and the locations are clean.
Add
free dining to a value room and there isn't even a discussion....