For us, it's on-site at UOR all the way. The amenities offered and the proximity to the parks and CityWalk can't be beat, and it's so
relaxing to not have to worry about anything. I agree with the
@Mad Dog on the "leisurely vacation" feeling--UOR is such a different vibe from Disney, and everything is so close, it's very easy to switch plans or just spend half the day lazing in bed or by the pool. I need my vacations to be as relaxing as possible, even when I'm going to theme parks.
We only go to Universal, so it makes little sense for us to stay off-site and have to drive in and park. And the caliber of hotels across all price points, at much more reasonable prices than on-site offerings elsewhere, is unmatched for our needs.
As for AirBnB-type services, we made a conscious decision to never use them many years ago, even if it means spending more money at a hotel. For us, the cost-savings isn't worth knowing (first hand) what this business model does to communities and the people who live and work in them.
And, well, I don't want to go on vacation just to have to cook and clean up after myself and others for the entire trip. Hotel amenities and services, please; I'm not here to work.