My vote goes for beautiful maps. Sure, a well-designed dungeon is good for the soul in most cases, but let's face down the nature of the game; Pokemon is designed around frequent random encounters and a turn-based battle system. This can make long dungeons, even the most intuitive and challenging, with lots of features, seem tedious and boring. Beautifully drawn and perhaps even animated maps, however, bring the game to life. Though, I may be a tad biased. I play hacks on GPSP through a very cramped memory stick, so getting more bang for my megabyte is very important to me.