I would say, whatever your company says !
However, having been on the ATC end of some spectacular level busts with climbing aircraft failing to set Standard Pressure, I would say, once cleared to a FL on the climb set 1013, once cleared to an altitude on descent set the QNH (which you will have just read back).
In all my years at Prestwick Centre up until my retirement in 2016, I have only been asked for the Transition Altitude or Level on a handful of occasions, but we had a handy table of minimum usable levels according to the pressure, so it was all pretty academic most of the time, under radar control we ensured separation and terrain clearance.
Having managed to blag my way onto many jump seats over those ATC years, mostly European airlines, I cannot recall ANY pilot calling out "passing transition altitude/level, setting 1013/QNH" but I do remember seeing them do it once cleared to a FL or altitude and both crew setting altimeters and cross checking.