If you're looking for miles rather than status, AS is worth a look, as you can put both AA (and most other OW) and NW/DL/CO on there, and you only need 50k EQMs to get to 100% bonus - though you get a satus match and get the bonus from the get-go. NW/DL give EQMs and get the bonus, CO doesn't. Also has one of the best partner networks - combined with UA you could book awards on pretty much any airline.