Many thanks to all of you for the informative replies (and apologies for the delayed follow-up; I think I was expecting a notification email in the event that someone replied to my post and thus neglected to log back in to manually check for responses!).

I currently have just 465,000 lifetime miles in the Aadvantage program, so it would likely take me at least 10 years to reach 1MM and thereby secure Gold status for life. Given this, I would think that lifetime mile benefits should probably not be the deciding factor for me, as I expect to fly a minimum of 25,000 miles every year going forward (and hopefully closer to 50,000).

It sounds like there are some strong cases for switching to UA/CO or DL. I have heard casually from some friends that the Star Alliance is greatly superior to the SkyTeam alliance, though I don't know the specifics of that argument. Can anyone weigh in on this issue?

Thanks once again!