I think it's best to look forward/up as much as practical. In other words, when it's useful or fun to look down or to get out of horizontal trim (e.g., on a wall drift dive), then by all means do what makes sense, but the default position should be horizontal and looking ahead. There is so much up ahead of us that we need to keep an eye on, and not just with peripheral vision. Our buddy, and if diving in a group, other divers, for example. If the bottom is highly contoured, we're also looking ahead to follow the contours. In some places, there could be hazards such as lines or kelp. And of course when diving along a wreck you don't want to be looking down all the time or you'll run into something. The downside is that it indeed can cause neck discomfort. It sounds like the OP has found a way to mitigate it by turning sideways. Nothing wrong with that.