AA, DL, and UA all have ok coverage, DL has a little bit more exposure by having 3 hubs (DTW, MSP, MEM) in the area.
Based on the expected flights, I should be able to get 50K+ MQM for 2011, and ~100K for 2012. So the question becomes the likelihood of getting upgrades.
For DL, it will be the SEA-DTW leg.
For AA and UA, it will be the SEA-ORD leg.