From the info I have gathered on the Net, it would seem like the PSP version is the best, content-wise. It is, however, litered with bugs that weren't in the original Playstation release. I want to know if those bugs are serious, as I am thinking of buying Dracula X on PSN.

I have run into one bug, which was quite serious: When you've broken Shaft's spell and proceed to teleport to the inverted castle, the game always freezes right after the movie sequence, making it impossible to get to the second map. 
 
I only ran into it on my second playthrough though, and I'm sure there are guides on how to avoid it online. Aside from that, no bugs whatsoever.

Using the two "extra" (They aren't really extra. They were in the original Japanese version.) familiars can lead to the game crashing, especially when you're around the area in which you fight the Succubus. Also, while you can play as a more Rondo-faithful version of Maria in the PSP version, she's gimped as fucked, and her game's also very glitchy in spots. It was really, really pissing me off trying to go through the inverted caverns as her, because running would cause me to get hit AND take damage when there was absolutely nothing there to damage me. If you want a more COMPLETE version of SotN, then play the Saturn version. Also, while I don't generally condone piracy, there's an extremely well-done English fan translation of the Saturn version that you can play via emulation. Definitely worth it.

As much as I love the Saturn version, though, it doesn't have the awesome voice acting of the U.S. PlayStation original. The PSP version's new translation wasn't just unnecessary; it basically feels as though they went through a thesaurus and reworded a few phrases and thought that it'd be better. While the overall quality from an acting perspective IS better, I'd say that some of the voices in the original U.S. release were good enough that I'd prefer the shortcomings in the original translation just to have the good aspects remain in-tact. Besides, how can anyone not love the original U.S. version's dialogue?