Originally Posted by urww

hotturnip, well if you're choosing based on redemptions, then you just need to check award prices, taxes and availability on the routes you're interested in and decide for yourself.

If mainly your miles will be coming from Chase and Amex I believe you would better stick with Delta. Though:
1. FlyingBlue awards cheaper from the US to Europe, Caribbean.
2. FlyingBlue adds 'fuel' scam charges, so if you are to take Air France from Atlanta to Paris and back you would pay 60,000 miles in Y + approx $50 redeeming SkyMiles or 50,000 miles + approx $200 redeeming FlyingBlue.
3. FlyingBlue doesn't add fuel charges for Delta direct flights from the US to Europe (so if you'll be flying Delta from Atlanta to Paris you'll be paying 25,000 miles + $20 redeeming FlyingBlue or 30,0000 + $5.60 redeeming SkyMiles).
4. Availability on AF and KL is much better with FlyingBlue.
5. Domestic redemptions are much better with SkyMiles (expect to pay 5,000/5,500/7,500/9,000/11,000/12,500 miles per one-way with SkyMiles while with FlyingBlue that will be always 12,500 miles or no seats)
6. FlyingBlue allows 1 stopover and a way more relaxed routing rules.

Think what works better for you in terms of awards you're going to be redeeming for.