I am approaching achieving lifetime PLAT status on AA, with 2M miles, and am looking to begin agressively accruing points on another airline. I am most concerned, however, with making that effort, only to have the airline go out of business, or otherwise make this new block of miles worthless (or nearly so).

So, if you were just starting out, what program would you choose, given concerns about loosing miles, and once accrued, the usability of miles globally. If you're kind enough to make a recommendation, please say why...

Thanks!
John