Best airline frequent flyer program is united (premier 1k or global services), followed by American followed by delta if you are Diamond (given I am NY based and where I travel for leisure, I prefer Delta ), below Diamond, its not much use. Also, not much use for redeeming for international flights.
BA is a good program, but only if you redeem on flights other than BA (Cathay, American).
Criteria is ease of getting business class redemption on flights at the lowest miles. The biggest bang for the buck is to use miles to redeem the business class or first class international tickets, not domestic flights (exception is Delta, whose redemption cost in terms of miles are substantially higher than others).