If you could reset your mileage meter to zero, and could pick one program to be loyal to, which would the best be in terms of upgrades (domestic and international), mileage bonuses, service, lounge access, etc.? I assume ease of mileage redemption and partner network should also be in the equation. Let's make some unlikely assumptions that you live in a major hub like New York or Chicago, with access to almost all major airlines, and that your company doesn't care which airline you fly?