By choice I don't fly on race-for-your seat carriers so can't comment on carriers without seat allocation. As for the others I tend to try and assess at the gate how full the flight is going to be. If it looks heavy I do my best to get on early so that I can guarantee a space in the overhead locker. Otherwise I stay seated and board at my leisure. I also check what type of aircraft I'll be flying on as hand baggage size is more restricted on the commuter types.