it depends on the case design.
you want slight positive pressure, but not so much that pockets of warm air are forced into regions of the case where the warm air cannot be cycled out of the case efficiently.
considering that the most common mid sized or full sized designs these days have front, top, & rear ventilation;
3x front fans drawing in cooler air,
1x rear fan expelling warmer air,
and 1x top-rear fan also expelling warmer air
usually is best common setup.
using a 240, 280, or 360mm liquid cooler in this type of setup the best option usually is;
3x front intake fans,
1x rear out-take fan,
and the radiator positioned on/in the top of the case with it's fans blowing air out through the radiator.
also, the PSU should have a vent under it in the bottom of the case. the PSU's fan should be facing this vent so it can pull cooler air into itself and exhaust that air out through it's own rear vent.
any particular case you are interested in may be different, so the setup would need to be re-evaluated based on that case.