There are indeed two bonuses for AA, one for 500 miles for any credit card and one for 1000 miles for a Citi/AA credit card.
The link for the 500 mile bonus is :
https://aa.rewardsnetwork.com/regist...017&src=arm305
The link for the 1000 mile bonus is :
https://aa.rewardsnetwork.com/regist...305?src=acm305
You must register at one of the links above to receive any bonus. My guess is regardless of which credit card you have, if you register with the 1000 mile bonus link, you will get the upgraded bonus.