I am flying to Paris from the US in April. What is a good airline to fly with?
Well the US is a big place so the routes and timing and cost can vary a bit, and that is probably the determining factor.
From the European airlines I like Lufthansa best for long haul as service is ok, aircraft new. Personally I am not a fan of any of the the US airlines as the service is often poor and the aircraft quite old, but if you are connecting from a domestic flight then this might be most convenient. If you can do the long haul leg on one of the middle eastern airlines like Qatar or Asian like Singapore it will be a good experience but likely expensive. For connections likely Air France is most convenient as the national carrier usually has the best timeslots.
Sorry to not be more specific and enjoy your trip.
Lufthansa is not operating US to Paris direct, there will be a stopover in Germany.
Aircraft are mostly new, but some are older (e.g. a few 747 and some Airbus A340), but that doesn’t matter.
Personally i would choose one with a direct flight on times which are comfortable for me.
As you did not write your origin it will make it more difficult
As mentioned above Qatar and Singapore Airlines are excellent.