AMEX SPG allows for great hotel redemptions as well as a great rate into AA miles (20k points into 25k miles). It's a 1:1 spend so it works out to be better than the AA Citi. Spending $7,500 a month will also give you SPG Gold and a reasonable amount of points/miles every year.

I spend similarly to you (~$5k per month combined) and I use SPG Amex and Hilton Honors Amex. Combined I have gold with both programs and earn points faster than I redeem them. However, I don't use them for AA miles since I fly a lot and can generally earn miles faster than I redeem them (butt in seat method).

I'm not much a Marriott fan and try to avoid them (I find their entry level properties to be far less attractive than Hiltons (e.g. Hampton>Fairfield, Embassy>Courtyard, etc.). However, I gained that opinion a long time ago and never really gave Marriott another try so take it for it's worth. I will say, in the past three years I stayed at the JW outside of Phoenix and the Grand Marquis in Times Square and both were great!!! However, I've had too many crappy nights in Fairfields and Courtyards, and I think Hampton and Embassy are best-in-class products. For upscale, I'm a Westin guy!

Finally, welcome to FT (this place is great)!