I thought Anguished Unmaking was fine, but unnecessary. There's a lot of great 3-mana removal spells floating around from O-Rings / Hero's Downfalls / Vindicate variants. Instant speed is nice, but 3 life is a lot, especially for black which already is inflicting itself a lot of pain. Regardless, I like Lingering Souls / Sorin over Anguished Unamking.
IMO, top 3 for Orzhov is Vindicate / Lingering Souls / Sorin, Lord of Innistrad. After that is when the conversation really starts.