The OP mentioned a big part of his decision is based on availability with partenaires. FB is not the best programme for that, with certain exceptions (domestic China comes to mind).

If TATL redemption on AF/KLM/DL metal is the biggest factor, then FB makes sense. If trying to make status, less so. And if he tries to redeem his FB on a transcontinental DL flight from JFK to LAX..........bonne chance.