Buying a D&D 3.5 supplement to update to Pathfinder.

[Private Sanders]

I like dark stuff, so I'm highly considering one of the following:

Heroes of Horror

Libris Mortis

Book of Vile Darkness

Can anybody who has one of these books tell me which is best or will update to Pathfinder best? I am interested in new core and prestige classes and monsters, and I also like new spells and class variants. I have no interest in new dieties or creatures of the outsider subtype (I don't use outsiders in my campaign very often. I prefer native threats.).

I can only get one book right now, and it'll probably be a long time before I get another, so I want to get something good.  

[Arc Vembris]

Heroes of Horror is the most player-centric of these. BoVD, a 3.0 product, is crazy with Outsiders. HoH also has great fluff advice for running horror games of any system,  

[Disciple of Sakura]

Of the three, only Heroes of Horror has new base classes. I'm not a fan of the BoVD, myself, but Libris Mortis is alright if you like undead. The downside of Libris Mortis for Pathfinder, however, is that undead in Pathfinder were extremely rewritten, changing hit dice, BAB, abilities, and in general making it difficult to 100% accurately convert a 3.5 undead without rebuilding from the ground up.

Though most of them could be used straight, if you really wanted to.  

[Arc Vembris]

Disciple of Sakura

Of the three, only Heroes of Horror has new base classes. I'm not a fan of the BoVD, myself, but Libris Mortis is alright if you like undead. The downside of Libris Mortis for Pathfinder, however, is that undead in Pathfinder were extremely rewritten, changing hit dice, BAB, abilities, and in general making it difficult to 100% accurately convert a 3.5 undead without rebuilding from the ground up.

Though most of them could be used straight, if you really wanted to.

Also, half-vampires