ePSXe, but better than that, ePSXe 1.5.2 (older). Why? It's very customizable and compatibility is good. With pSX, you get even better compatibility, but it's not customizable. You can't change screen resolution, graphics quality and other stuff to keep compatibility at a maximum level.
Oh, by the way, why ePSXe 1.5.2 and not 1.6.0? The latest version has some boot and compatibility issues.