I was actually taught route-up in the military- which just goes to show that it must depend on the actual instructor's own preferences. When I started flying I tried route-up and my first instructor advised north-up, which I still use (it is much easier to read the writing!). I tend to write a lot on my maps so keeping it north-up is necessary to read the various prompts I've made for en-route. North-up is not really hard when you're following a big black line on the map, although I have my GPS set route-up.