AA has a daily nonstop JFK-SEA (and reverse) flight. Most others are connecting flights (yes AS has EWR nonstops also).

AS is a partner airline where you can earn miles (and EQPs toward status) based on this information . However, the traditional One World features (cooperative lounge access, enhanced checkin lines, etc) do not apply on Partners.

500 mile stickers also do not apply on Partners (nor on OneWorld).. they apply only to AA metal.

Upgrades are pretty non-existant on Partners as they would upgrade their tier fliers ..

I guess the issues you need to choose...

The nonstop AA from JFK
The ORD or DFW connections (or others tho this might include an AS flight)

I am not a big fan of the 757 that is operated on the nonstop route (tho 757s are also on the connecting flights). I would probably go with the connectings anyhow ..

Get the PLT Challenge going with your first flights. Until you get PLT-Lite you might consider a couple full fare flights to get non-tier comp upgrades at the 24 hour mark ...