I don't know your origin or destination, but assuming you're looking at a two-segment USA-JFK/CLT-EUR, I'd lean toward the CLT connection for two reasons:

1. Fewer ATC problems at CLT.

2. Another hour of potential sleep on the overnight flight.

That's unless you're starting from LAX or SFO, in which case I'd opt for JFK with the 321 Transcon birds versus ghetto PMUS 321s. Or just connect at LHR.