If moving to North America, I would suggest you look at the AC program, I think it is very good, but I would consider where I would be flying once I am there. If you think you will be doing the European runs, I would stay with BD, so that when they fold into LH, you are already involved. The key to your American program will be decided by your choice of American credit card IMO, so do a little homework before you go, picking the right cc and getting bonuses, can mean a big difference