If you're deciding between the Gellert and the Szechenyi bathhouse, I would choose the Gellert due to its central location. I also think the Gellert smells less of sulphur and isn't as crowded (at least not on weeknights). Everyone knows this is an ornate and luxurious experience but the highlight for me was the wavepool. Brought me back to my childhood! There is also a snack bar and terrace that overlooks the outdoor bath. Run, don't walk kids!