There are pros and cons to both. British Airways business class is very good and consistent (flat beds). But the problem is that you will have to stop and change planes in London, which is always a bit annoying.
Air France business class is inconsistent. In their Boeing 777 and A380, they have full lie-flat beds. On the other hand, in the A330 (type of plane they fly from Seattle), the seats are lie-flat, but with a 170 degres angle -- which some people find quite uncomfortable). Hope that helps!

Echoing m22's comments, British Airways' Club World is superior to Air France's Class Affaires. However, for business travel I always prefer the nonstop over the connection. So, if your choice is Air France nonstop business class on an Airbus A330, or British Airways 777 connecting in London, I'd do the direct flight every time.