Right now there is a 25% off deal from Disney. AAA rate is 10% off, so you're better off booking through Disney directly. If you want the package deal (including park tickets) then AAA offers a few extras, in addition to the 25% off.
FWIW though, I've had continuous AAA membership for 20 years. The Disney travel benefits are nice, but they're not why I use AAA. The hotel discounts alone (for places all over the world) are significant enough to more than pay for the membership. The free maps are a nice plus. And I like the free 'emergency key' they provide for my car, the free towing and other emergency roadside service. We have also gotten discounts at other theme parks and vacation areas by flashing a AAA card. Of course, it's different for everyone, but I find that the membership is worthwhile. Keep in mind that it costs a lot less to renew than it does to 'initiate' (i.e. first year of membership costs more).
Hope that helps.