I fly ORD-CDG a lot and am usually upgraded to C. My experience with these crews has been excellent with one exception. In the exceptional case there was a screwup and I had an F seat downgraded to C, moreover the C seat I got was 10E. My guess is that my complaints at the IFC lounge got noted somehow so one of the French FAs was fairly gruff with me. She even made a remark about "people who can afford vacations in business class while our pensions and salaries are cut", i.e. totally out of line. I chose to sympathize with her over the cuts and point that in fact I was on a businees trip. All of a sudden my service improved. A little bit of honey (as opposed to vinegar) can go a long way. FAs are people too. Afterwards UA made good on the F seat screwup with a CS issued SWU and I was content with the outcome.