Asking for my septuagenarian widowed mother. I think I'm deciding between BA, AS and AA but maybe I'm missing something.

(1) What is most important to you in a FFP?
Miles not expiring due to inactivity; getting some sort of value (tiny discount, ability to redeem miles for ancillary benefits) without too much effort learning all the ins and outs of the program.

(2) How many miles do you usually fly each year & in what class? How many flights/sectors?
Under 30,000. Domestic within Canada and one or two transatlantics. Usually in Y or in PY if not too much more.

(3) What types of fares do you usually buy?
Economy.

(4) Can you choose your airlines and/or class of service? Do you travel for work and/or pleasure?
Pleasure. Most travel would be AC, but need somewhere to dump the BA miles when the schedule/price is more appealing.

(5) Which routes and airlines do you fly most often?
AC YYZ-YEG, YYZ-LHR

(6) What is your home airport?
YYZ or YXU

(7) Do you have FFP status of any kind in OW or other airline? What is it? Do you have any miles banked in a FFP?
None.

(8) Preferred Airlines? Most common Airlines flown on?
Air Canada, WestJet (I know, not relevant to OW).