I just recently took the Delta SEA-AMS in Delta One and thought it was a good flight. I would also suggest a stopover in Amsterdam as a really great option--one of my favorite cities in the world.
Another option to consider would be KLM nonstop from SFO-AMS, and then connect on KLM. They fly both 747's and 787's on this route, so both interesting aircraft options. The 747 is bit dated but the many people like the Dutch service, and you also get a collectible porcelain Amsterdam house filled with gin as a departing gift.
Note that the KLM lounge in SFO and the Delta lounge in SEA are not great (though Delta is much better), unless you fly from SEA after they open the new Delta lounge, in which case, it will be fantastic and could be one really nice feature of this flight.
If you connect in LHR the taxes could be higher (or is that only for o/d)?