AMS would be the easiest airport to connect through. However, Air France and BA would have far better service. My partner has been flying NW from SEA to AMS in WBC. He's sent in so many complaints about the horrible inflight food and rude flight attendants that NW has given him 40,000 miles in compensation. In the future, he'll use AF to avoid having to fly NW WBC.

AF has been advertising some good sale business class fares from SEA. When my partner looked at BA, they have always been significantly more expensive. We flew AF from SFO to VCE last year, and really enjoyed the service. Some people do not like AF service. In any case, one would be hard pressed to say it was worse than NW.

As for CDG- it is a bit of a hassle. However, it has a very nice arrivals lounge for business class passengers to shower and have breakfast, even if you are just transferring through CDG. Depending on when you are going, parts of the new S3 should be open and make it a bit easier. Also- if you have a tight connection AF will drive you from one plane to another. They did that on our return, and it was a really nice service. CDG is a bit of a mess right now, but AF is doing a lot to mitigate it. Once S3 is finished and 2E is rebuilt, it will be a much better airport for connections.