Please let me know if I'm missing anything or anything I state below is incorrect.

I've decided to go with a card that earns miles over a cash back card (Capital One Venture) because if you redeem your miles efficiently, you can effectively get 4-5 cents per dollar you spent.

Among the different airlines, it seems you get the most for your miles on AA. While I like the fact that you can earn status miles/MQMs on the Delta/Continental cards, you can't earn significant status points just on your cards, but you must also be flying a lot. (For example, with delta platinum card you get, 10k MQMs when you spend $25k and another 10k MQMs when you hit $50k...but you need 25k MQM's to qualify for their lowest level silver status so spending $50k on the card doesn't even get you there). As a result, I like the fact that every dollar I spend on AA counts towards my million mile/lifetime status (whereas only status miles count on other airlines). As I usually don't fly more than 6 times a year, I'm not flying enough to hit million mile status on any of the other airlines that don't allow you to do it with credit card spending.

That brings me to the choice between the AA Citi Cards and the SPG Amex card:

With AA you're earning 1:1 mile per dollar spent and you're getting a 100k mile bonus if you spend $10k during your first year. With SPG, you earn 1.25 points per dollar get 25k bonus (10k points to sign up and another 15k after spending $15k during the first 6 months). So basically, you're earning more miles per dollar with the AA card up until you've spent $275k on your card. At that point, you'd be at 375k miles no matter which card you chose. After that, you'd be earning more miles per dollar if you went with the SPG Amex. (If you think you won't earn the extra 15k bonus on SPG for $15k spend during 6 months, the break-even point is $350,000 spending).

SPG Advantages:
- Being able to transfer miles many different airlines (1.25:1)
- Transferred miles still count towards your million mile or 2mm mile AA lifetime status (I'd probably transfer all my miles to AA anyway)

AA Advantages:
- Annual companion ticket (do you also get a companion ticket for every 10k you spend?)
- Discounted reward bookings (some flights cost less miles if you have the AA card...not sure how limited these discounted bookings are)

Given all this, my plan is to sign up for the AA Citi Visa until I hit the $10k spending required to get the bonus, then sign up for the SPG Amex and use that everywhere that accepts Amex. In this case you end up with 472.5k miles after spending $10k on the AA visa and spending $265k on the SPG rather than the 375k if you spent all $275k on one or the other. You also get all the advantages for both cards that I mentioned above.