Starpoints can be converted to airline miles which can be redeemed for upgrades. ThankYou points can be redeemed for airline tickets, but not for upgrades. (My understanding from your original post is that you are primarily interested in upgrades.)
In most cases...
$20,000 spending = 20,000 Starpoints = 25,000 airline miles
(Notable exceptions are Continental, Singapore and United, where $20,000 spending = 20,000 Starpoints = only 12,500 miles.)
Also, Citi can change the ThankYou point redemption schedule at any time, and previous changes have been quietly announced only with only about two weeks notice. This can devalue the program for travel on every airline simultaneously. By comparison, Starwood typically announces changes well in advance, and it seems less likely that every airline partner would devalue mileage redemptions at the same time.
thank you so much but if AA is the best choice to do upgrades, wouldn't it be better to just get the AAdvantage CITI card? now they have 25,000 bonus..