Scots,

One of the biggest distinctions that I see, which only applies if you plan on doing osme significant flying or charging a lot on credit cards, is their "easy" to obtain lifetime programs. Just earn 1 million miles and get lifetime gold, 2 million gets ou lifetime platinum. you should be able to do this much quicker than 1 million actual miles on UA to get lifetime Premier Executive. AA's top level (Executive Platinum) is amazing (great service, free upgrades domestically on B fares, etc.). But if you are doing lots of A/P travel, then UA is the way to go.