We stayed at AoA and loved it. It's so cute with great theming. Also the rooms aside from Little Mermaid have two rooms and 2 full bathrooms which is great for a family of four. As a note, there is a quick service place (with lots of selection), but no table service. Didn't bother us, but may be a factor for some (but probably not for you either since you're looking at offsite)
I forget the numbers now, but if you say onsite there are advantages of being able to book your ADRs earlier, FPs earlier (and for all your nights at once), visit extended hours, and free parking. It's definitely an advantage staying onside at Disney World.