I've taken a UA 777 SFO-CDG. It isn't bad. You have a personal tv and food is good. The seats are ok, although I don't think all rows are equal. Some rows, particularly in the center section, are more cramped than others. So watch out. If you get a good row, the pitch (32") is decent.
I have no experience with either AOM or AF. But I don't imagine AF would be THAT much better than UA, so I guess you can determine whether the price differential is worth it.
You probably know this already but just to mention quickly...I hope you're using a good travel agent or a consolidator vs. booking direct with the airlines. The price differences can be extreme. I'm currently planning a trip to India and the differences between published fares and consolidator fares are approaching $1000. Anyway, sorry if I'm telling you something you already know. Hope you have a nice trip -- Paris is amazing.