Under is very popular here in the Netherlands where i live now. I actually find it correct when the loo is very cramped. When the restroom is so small you are touching the TP roll with your legs, it's easier to unroll when the TP is farther from your leg.
It was strangely interesting to read. I mean I understand people have their views but now I know that there have been studied, University classes, and so much more. All dedicated to freaking toilet paper. It feels a bit like an episode of community.