Depends on what time of day you want to fly as well.

NW has a 3p departure to MSP, which connects to a 920p departure to AMS. From AMS you'll have several choices into Rome on KL. There's also the direct SEA-AMS flight on NW which leaves around 115p.

However, BA runs two daily flights from SEA. One departs around 645p (747) and another at 845p (777). Of course you'll have several LHR-FCO options on BA. IMO, these are the easier flights to sleep on because they depart later.

I don't know AF's schedule at CDG but AF does not fly from Seattle. You will have to take Alaska down to SFO and then connect or take DL to JFK or ATL and connect to AF across the pond. Again, these flights will require that you leave earlier in the day.

-RM