Going through Under Cover Tourist or by purchasing them at the gate and using a AAA discount? I heard tickets are cheaper when purchasing at the gate and using a AAA discount. Can anyone confirm this?
Tickets purchased at the gate will be the most expensive way to go.
AAA tickets must be purchased at your AAA office or thru their website. You cannot "show your card" and get a discount at the gate.
Undercover Tourist is definitely the cheapest source of the 3 that you listed. If you sign up for the MouseSavers.com Newsletter, they almost always have a link in it for discounts at UCT.
The only exception to this would be 1- or 2-day MYW base tickets. No one discounts those. Your local AAA probably doesn't even offer them (mine doesn't) and UCT will charge more for them than Disney will.