AS is a good programme, especially if you anticipate lots of travel on AS/DL/AA. They partner with lots of other good airlines too like KE, BA, QF and CX but you don't earn EQMs on those and your status means nothing on them.

Seeing as it looks like a lot of your travel will be over the Pacific and are based out of SEA, I think the best airline programme for you might be DL. DL is the main TPAC operator out of SEA and you can connect pretty much anywhere in Asia on SkyTeam in ICN or NRT. You can even get to Oz on DL through LAX and earn miles while flying AS domestically. SkyClubs are also the "best of the worst" as far as US airline lounges go.

UA is also worth considering seeing as UA and *A are so huge and pretty much well-connected anywhere in the world. To be honest though, I think DL is a better airline to fly (not counting FFP) than UA. I'd stay clear of AA/OW in your case since AA's TPAC routes are pathetic and CX/QF don't operate to SEA.