While only somewhat related to your question, I would recommend getting as many Citi AAdvantage Executive cards as you can (and yes, you can churn them, see the related thread). If you are interested in international business class flights to Europe and Asia, then United is the lost cause after the devaluation.

The reason the Executive card is still related to your question, is that it requires $10K spend requirement in the first 3mths. You can have 1 Citi card in an 8-day period, and 2 Citi cards in a 65-day period. It costs $450 but gives you 100K miles, $200 statement credit, and free access to Admiral and One World lounges. Get it/them until they kill the offer, as I expect they will kill it sooner rather than later.