I recently have shifted to Flying Club, mostly due to personal circumstances rather than any dissatisfaction with BA. I took advantage of their offering double XP (their equivalent of TPs) to get status fairly quickly, and am now up to Gold (equivalent to BA Silver) and should be hitting Platinum (equivalent to BA Gold) next year.
I have to say that the grass is greener in some things but not in others. I found that the UK call centre can be got to relatively quickly, although I have no idea if French or Dutch members experience what UK based BAEC ones do. On the other hand, the KLM Lounges at AMS are pretty dreary, especially given that they're supposed to be the flagship (they *look* good, but the offering is very subpar).
What I definitely don't miss is the drive down the M40, and AF Coffee in J is the best I've had on a plane. On the other hand, the KL long distance Y on the 777s are awful. BA's are much more comfortable. I guess my point is, any airline will be better in some things but not others, it's a question of finding the package that works best for you.