Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
The OP should also keep in mind that AS flies DCA-SEA and SEA-EWR, and those flights can earn Avios. However, AS flights will not earn BAEC TP unless they are purchased as AA codeshares. (AS also serves Bellingham -- BLI -- in case that is an acceptable alternative to SEA. Because BLI is primarily served by discount carrier Allegiant, AS might offer lower fares to BLI than to SEA.)
If the OP will be flying in Economy to/from SEA and is willing to forego the Avios, I would suggest also pricing flights on Southwest Airlines at southwest.com.