I think you really need to add up the costs. I booked through AAA because they had the free parking and some "bonuses" that I thought would be nice (MMTTM, priority seating at certain shows, lanyard & pin, character phone call with crush, and a $10 savings on our ariel's grotto dinner). However, I did not know about getawaytoday when I booked and the package through getawaytoday is about $400 cheaper than my AAA package. Parking is $12 a day so for 5 days that would be $60 -- a far cry from $400. So then you have to ask if the MMTTM and priority show seating is worth $340 (getawaytoday gives the lanyard & pin, a backpack, and SoCa coupons you can print from home).
I read on one posting here that someone thinks getawaytoday has the best prices on Wednesdays. Not sure if that is correct but just wanted to pass that along.
We booked through Costco. They usually offer "perks" as well. We got a free Character Breakfast as well as the TTMM, VIP seating for Aladdin, a $20 gift card, etc. No free parking though.
I priced Costco as well because they had all the similar perks. The character brkfst and gift card is definitely a nice perk but they were about $30 more than AAA and AAA had the free parking.