As I answered similar questions in the *A forum, my general advice without taking location/flying pattern into account would be:

<25k miles: A3 (low qualification threshold, and redemptions for intra-NA C and TATL F are decent)

20k-40k miles: TK or OZ (low qualification threshold, qualification over two years, OZ offers very generous 1MM status which counts flights on all *A partners)

50k-100k miles: UA/CO may be an option for those flying from Canada to/through the US (*G status, 100% miles bonus, UDU)

>100k miles: pretty much any program

BD is an excellent option if you pay for full-fare Y, C or F, but the program will be folded into M&M this year. If you can qualify for Gold status (55k miles when starting from scratch) until summer, this definitely is an option, as there is a good chance BD Golds will be grandfathered into the M&M SEN program (though possibly with fewer benefits than other SENs)

LH M&M SEN status (100k status miles every other year) isnīt that bad if you pay for C/F and offers some nice status perks like booking guarantee etc., but apart from that M&M sucks (redemption rates are ridiculous, award rules VERY restrictive, fuel surcharges on *A awards, one long-haul upgrade every two years; only good thing about SEN status is itīs valid for 2-3 years)

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Basically there arenīt that many good *A programs, Iīd therefore recommend to look at OneWorld:

BA: low qualification thresholds for those flying PE/C/F, redemption rates slightly worse than AP, 100% bonus for Silver/Gold members, upgrades using miles provides excellent value

AA: excellent program for EXPs (100k status miles/year): 8SWUs valid on all fares, UDU, very good redemption rates