You're talking about WDW, right?
We only stay offsite, have never stayed on. Probably done at least 15+ trips by now. We've looked at other websites, but the one that's far and away the best...IMO...is VRBO. You'll have endless variety and choices. AirBnB isn't bad and there are a few others, but VRBO is far better. The reason why, at least for us, is the variety. The other websites don't have anywhere near as many options as VRBO does. I never pay more than about $90/night for a 3 to 4 bedroom 2.5 to 3.5 bath condo/townhouse. Usually a bit less...including fees and taxes.
As for best area, Rt. 192 runs east/west along the south side of WDW. There are incredibly large pockets of townhouse/condo gated communities on each side. I'd highly recommend picking one of those. We prefer the east side, but have stayed on the west side many times and like it just fine too. You'll be 10-15 minutes tops from the "entrance" to WDW...then of course you have to get to the actual park you're driving to. Depending on where you stay, it may even be less.