I'm preparing a D&D campaign, and am unsure of what kind of materials I should use for the battle grid. At first I thought of using simple grid paper and to draw on it because I am good at drawing, but then I learned about erasable/reusable grids I could use. I am now unsure of which I should use, and my uncertainty is increased by the fact there seem to be a lot of different reusable grids.
I am looking for a grid that is:
easy to use
large in size
accommodates both planning maps ahead of time and on the spot improvisation, if possible
What kind of grid fits those criteria well?