I came here to say this! It really depends on if you have cats or not. Both are fine by me, I mean as long as someone doesn't just leave the empty roll and not replenish it, that's all that bothers me...
Oh and over is the right way... at least the inventor of TP thought so.
I have a cat but we still keep it over because 1. He can't come into the bathroom unless someone is there with him or the door is open 2. Even if the door is open and he is alone, the first thing he wants to do is jump into the bathtub, my cat couldn't care less about toilet paper lmao
Neither, actually lol.. I leave the roll sitting on the sink next to the toilet or on the back of the toilet itself. If I had to choose between the two, though, I'd definitely pick over. I have trouble tearing off the TP if it's under.