Aircraft (seat, etc.) type and comfort, connections vs nonstop, airport convenience, seasonal weather effects, time in the air, fare costs, flight frequency in case of IROPS, etc. are some of the variables that I take into consideration as well as lounge access. But this is true regardless of airline, and may affect which airline I take as well - AA, AS, BA, CX, IB, LH, QR, WN, or others.