I wouldn't stay on site if it were free...seriously. No way, no how. That's not meant to be an insult to onsite, just how strongly we feel about being offsite for our family.
It really can't be stressed enough how nice the extra space is. We rent a 4 bedroom, 3 bath 1200sq ft townhouse. It's got a full eat in kitchen, full family room, in house laundry, etc...plus since we're a family of 5, each kids gets their own private bedroom, which they LOVE. After a day in the parks, who wants to come back and cram into a small hotel room? It's so nice to be able to just relax. DW and I can put our feet up on the couch and watch TV while the kids are in their room watching videos. There's privacy for DW and I...
. We can go to the resort pool if we want, etc... We don't all share one bathroom, so we can get ready to go quickly. Just having that family space AND privacy is phenomenal.
Cost. We spend $700-$900/week, including all fees/taxes, etc... You're not getting that kind of space for that kind of money on property.
In house laundry. Sure, nobody likes laundry, but unless you're bringing a ton of clothes and packing heavy, it's so nice. Even for a 17 day trip, we only pack maybe 4 days worth of clothes. Laundry is ridiculously simple. Toss it in the wash when we're sitting down for dinner...toss it in the dryer after dinner. No ironing, or even folding honestly. It's just cotton shorts and t-shirts, so we just hand them back to the kids and we're done.
The kitchen. Everyone has this image of "cooking" on vacation and how they dread it. Well, it's what you make of it. If you want to spend hours over a hot stove, you can. But why would you? If you want, you don't have to cook a single thing, you could always eat out or order in. Or if you cook, like we do, make it simple. We'll throw some chicken in the oven or crockpot and just let it cook. Prep time is maybe 10-15 minutes, then it cooks while we're relaxing, showering, whatever. Clean up is just as simple...it's called a dishwasher.
We can also pack lunches, snacks, etc...or just keep that stuff in the house for when we come back from the parks. It's awesome to come home, open the fridge and grab some grapes, or the kids can grab some pretzels. I'd bet we spend less than 20-30 minutes per day total "prepping" food...and even when we are doing it, it's not heavy labor. It's light stuff and we're having fun...DW and I spend that time together talking, laughing, and the kids get involved too. Same with "cleaning". We don't polish furniture, scrub floors, nothing. That's why there's a cleaning fee for the house/condo we rent. After you leave, they have a cleaning service come in and clean the house. Sure, we pick up after ourselves, but you'd do the same in a hotel room. But unless we spill something, we don't vacuum, scrub, dust, etc... Heck, we don't even make the beds usually.
The area around WDW is awesome. Endless shops, restaurants, activities. You name it, you'll find it. Our "Disney bubble" is not only WDW property, but all the things around it, so we have more things to do.
Some people would say that having to drive to WDW instead of using buses is a con. And if you don't like to drive or want to drive, sure, I guess it can be a con. But for us, it's a HUGE pro. Just like I would never stay onsite, I would never rely on WDW transportation....it would be a deal breaker for me. We like to go where we want, when we want. If we want to go from Epcot to Typhoon Lagoon, hop in the car and go. Want to then go check out AoA, get in the car and go. No waiting for buses, transferring buses, etc... Also, no cramming into a packed bus. It's nice to have your own private ride...we control the music, a/c, etc... We'd never use the buses.
Offsite doesn't allow you to participate in EMH, but for us, so what? We never rope drop anyway, we think it's a total waste of time (no more "productive"), and for evening EMH, no big deal...we can go to another non-EMH park if we really want to be out late at night.
Offsite can only do 30 days in advance for FP+. But with very limited exception, it's no big deal.
I do understand why people swear by on property, conceptually I understand the attraction to it. But for us, it wouldn't fit. Offsite is the only way to go.