Originally Posted by MSPeconomist

I very much like Gardyloo's suggested strategy, but to answer the OP specifically about where to credit miles from SQ flights: I would probably avoid crediting to SQ because SQ miles necessarily expire after some time, IIRC three years, regardless of whether the account has been active. So even if you're continually crediting a few miles to the SQ FF program, your early miles start to vanish before you have enough to use.

It's better to avoid orphan miles and focus on a few FF programs so that you can know their rules well. You also want to have enough FF accounts to cover any flight that you're likely to ever take, so that rather than wasting miles, you always have some account where you can credit a given flight. This usually means one FF account for each alliance but AS fulfills this role well for many people and includes enough airlines to give nice redemption flexibility.