If you go on a lot of C/F trips Lufthansa is not a bad option. If you go a lot in discounted Y then that might be a bad idea.
Personally I'm with United and very happy with them. You get *S at 25k and *G at 50k miles. Awards are relatively cheap compared to Lufthansa, as a rule of thumb you get more miles with them in Y and less in C/F fares (again compared with LH).
A lot of people seem to thing BD is pretty good right now, but I just can't be bothered to switch over. Quite happy with UA.