The front gate, as thats where you pay for your AP. Guest Services is the best place to buy your APs, as they have more of a clue generally than the CMs at the normal ticket turnstiles (and usually Guest Services is quieter too).
Give them the sponsor form, they will stamp it there and return it to you, then charge you the AP fee minus 10%. You'll get a temporary AP, which you then take to the AP bureau in the park, where they exchange the temporary one for the permanent photo-laminated AP.
Give them the sponsor form, they will stamp it there and return it to you, then charge you the AP fee minus 10%. You'll get a temporary AP, which you then take to the AP bureau in the park, where they exchange the temporary one for the permanent photo-laminated AP.
DLPdaft has it exactly, only they don't stamp it here for you. They give you a receipt which you have to present at the AP bureau and once they have sorted out your AP cards they'll then stamp your form.