BB, since you ask:

BA Exec Club (oneworld), AC Aeroplan (Star Alliance)
and I believe I have a dusty Alaska card somewhere.

The rationale behind my choice: BA and AC offer excellent service in the air, take me to the places I want to go, and belong to the two major competing alliances, allowing me to gain credit for travel with their partners when I cannot fly on their own aeroplanes. Although I have yet to claim an award ticket, I believe that by focusing my travel with these two airlines I will
1) maintain/gain elite status and thus be given even better service, more privileges and mile-earning opportunities
2) be able to claim the long-haul awards I am really interested in - such as two BOS-CPT tickets next year

If, for business purposes, I am obliged to travel on non-alliance airlines, I will probably sign up for their ff programs - but I hope to avoid this.

I have no interest in collecting a wallet full of different ff cards: a large part of the reason why I enjoy BA so much is that, by flying with them regularly, I am intimately familiar with their style and system - and as a result I receive superlative service.