I do QSL via ARRL's Logbook of the World (LoTW) and try to upload the log as soon as possible, quite often this is directly after the QSO.
How to QSL our QSO?
LoTW is great but I prefer the classic paper QSL. Send your QSL via your QSL bureau/manager or via the Dutch QSL Bureau.
Dutch QSL Bureau
PO Box 330
6800 AH Arnhem