You get a decent number of redeemable miles for KLM/Flying Blue if you're booked into a higher fare bucket, and crediting to FB while on Delta metal gets you redeemables based on distance flown. The down side is that they've got a fairly quick expiration date so you need to continue to credit to FB once or twice a year to keep those miles alive. FB is lousy in terms of elite qualification if you're USA-based, but if you've already got ST status with another partner that's not much of a problem (exception- FB native status is needed to redeem for first class on Air France)

FB has a lot of credit card transfer partners and their promo awards often get you a good deal if you can be flexible enough to take advantage of them. but again the non-flight points have a two year expiration timeline if you don't earn or burn them, and non-flight miles are on a different expiration clock than flight-earned miles are so you have to check your account for that on a regular basis so you can feed it and not lose the miles.