To add to what Gemini said, pSX also handles hacked versions of games (such as the Chrono Cross Magil Patch) way better than ePSXe. The one thing I like about ePSXe is that its savestates work very well with Agemo's VRAM Viewer (VRAM being that portion of game memory in which active graphics data are stored); I'm sure there's probably a way to get Agemo's VRAM Viewer to examine pSX savestates, I just haven't looked it up yet.