There are many threads discussing this in this forum if you do a search.

In my opinion, for international economy, I think it's best to earn points on SPG or Amex MR and when you're ready to redeem you have the option of looking at several airlines for the lowest redemption rate and then transfer to that airline (or a partner of that airline that allows you to book into the airline of your choice). Between all the airline choices you have for mileage transfer you are bound to find one that will have availability at the lowest redemption level. I usually find that standard economy awards are not all that hard to book. Now, if you're going to talk about C or F awards, that would be a different story...

SPG Amex has long been voted by most as one of the best Amex cards to have due to the versatility of it's rewards program, and I'm a big fan of it.