Whenever I add a FF program it's because the airline is going to be convenient for my travel pattern. When I lived in MSP, NW (now DL) had a fortress hub both there and my most frequent destination (DTW). My employer has a preferred contract with UA (used to be much more preferred, now they've diversified more) so I signed up with theirs. I signed up for AA mostly because they had a convenient early flight DTW-SAN on dec 26 and it looked cost effective to accumulate CC miles for that, but they changed it so I don't fly them much. My partner recently got a job in PDX, so I fly AS a lot and joined their program (and got a status match from UA). Southwest I joined a long time ago but I don't think I've ever redeemed miles - they're convenient for short hops out of LAX/BUR. I don't really pick an FF program based on what they offer - it can change at any time. I picked based on my flight patterns.