For dungeons, I do pre-drawn maps on grid paper, glued to cardboard, cut into tiles, per room, that I can place down as my players explore. I think having something like that makes the game more exciting and dramatic. It also lets me build more complex puzzles. My last map had minecart tracks all throughout that the players needed to use to move a piece of mining equipment to a certain spot to unlock a secret area. If I hadn't had it prepared in advance, describing it specifically, or drawing it on a whiteboard, would have made it too obvious, I think.

For more open stuff though, like exploring a large aboveground region, or minor standalone encounters, I think theatre of the mind works well, and saves prep time, which is important. For games that rely more on the battle map, like PTU, which is what I actually GM, something like a dry erase board with a grid works well in these cases.