I don't think there is any one correct answer here, it all depends on the design of your particular gate, stairs and landing.
Personally, we don't close the gate when we're downstairs (because if the toddler did make it upstairs without us noticing, we want her to be able to get on to the landing and not be thwarted by a gate!) so the gate is only closed when we're upstairs. Given this and the design of our particular stairs and landing, it only makes sense for the gate to open "outwards" over the stairs.
[I should add that our gate is NOT a pressure-mounted gate, and I would not use a pressure-mounted gate at the top of stairs in general. Ours is bolted into the wall.]
Edited again to add a picture:
The top stair is large and square (like a mini landing) and then when you come round the corner you are immediately at the door to the bathroom. The green line on the picture is where there is a balustrade rail preventing anyone falling off the edge of the landing. As you can see, if we had fitted the gate to open "inwards" onto the landing it would have clashed with the bathroom door. However, having it open outwards over the stairs wasn't an enormous risk in this situation because of that large flat top stair.