This is an essential point that many new FT members completely misunderstand: It is absolutely essential to understand your own travel patterns.

Let's say you want to purchase an international F ticket that prices at $4050. You can also book the ticket with 125000 AA miles. Let's say the actual journey is 10000 flying miles. You'll lose the opportunity to earn those 10000 if you use an award ticket, so the real mileage cost is 135000. Using an award, in this case, would value AA miles at 4050/135000 = 3 cents per mile.

Using the SPG card, you could earn those 135000 AA miles by transferring 108000 starpoints. If you earn 1 starpoint per $ spent on the AMEX, then your return is:

4050/108000 = 3.75% by using the Starwood AMEX. That's a great return.

HOWEVER. This math is only valid if you would actually purchase that international F ticket. For many of us, our travel pattern is primarily domestic economy class. For us the math is different:

Let's say I want to purchase a $360 domestic ticket. The award would cost 25000 miles, plus the lost opportunity to earn 5000 miles = 30000 miles cost. If I use an award on AA, that values my miles at 360/30000 = 1.2 cents per mile.

Using the SPG AMEX, I'd need 24000 points to convert into 30000 miles. 360/24000 = 1.5% return on the SPG AMEX.

That's still a decent return but can't beat a 2% cashback card or the Southwest/Virgin America Visa cards.

My point is: you have to know what you would actually use your miles for. Otherwise it's meaningless to ask anyone which card is best for you. Once you know what an AA mile, for example, is worth to YOU, you can (fairly) easily calculate which card is best.