Technically? If you're on a GMRS radio, you're supposed to use your callsign.
Practically? On simplex? Just talking amongst 'your group' (as you would be here) and not talking to random people out on the airwaves? As far as anyone else knows, you're on an FRS radio too.
Out hiking, at the race track, on a road trip and only talking within our group, we just use names.
Talking through a repeater, I always use my CS. But 99% of my use is simplex talking to friends & family.