Sorry to throw cold water on this, but you're aiming a bit high if you expect lifetime status with anyone after 12 months' flying. Even with AA, which counts all miles from all sources, that's probably at least 400,000 butt-in-seat miles to reach a million total. While I'm sure a few people have flown more than this in one year, it's pretty rare. With other airlines, you'd need the whole million as BIS, which is well-nigh impossible.

So, I think your practical choices are AA and perhaps CO, depending on how big a head start your previous flying with them gives you. Just don't expect to finish in 12 months.