I'm still digging into the PC-FX library myself, so I'm probably not experienced enough yet to make qualified recommendations for its best dating sims.
This is just a random aside, but my favorite dating sim, oddly enough, is a game on N64 called Getter Love!! (it's the only true dating sim in the N64's entire library). It's this really bizarre hybrid of a dating sim and a board game. It can be played with up to four people, but even playing alone with three AI opponents, the competitive angle really makes it a ton of fun. Of course, given its nature, it doesn't have the depth of story of something like Pia Carrot.