I'd have a tough time deciding between the NYT and WSJ next, especially since the editorial/opinion section of the WaPo is the least valuable to me (informed opinion is something you can get everywhere on the Internet for free).

(WaPo vs. NYT was basically a coinflip decision for me, but doing WaPo and then NYT would probably create a pretty significant overlap, and WSJ wouldn't. On the other hand, the NYT is a substantially better site than WSJ).