Which way do you place your heater?

I’ve always placed it as it says on the box, so horizontal.

Out of habit in dealing with older heaters that weren’t fully submersible - I’ve always placed all of my heaters vertical in my tanks (preferably close to the intake or outlet of my filter(s)).

Being someone that has never needed to use a heater I haven't needed to place one in any position but if I was to have a heater that I needed to place, I would definitely place it horizontal rather than vertical mainly because it just looks better horizontal and it looks as though the heat would reach more areas in the water horizontal. I know friends that I have that have used heaters, they always have their heaters horizontal so that must be the norm for most people.