Tough question. From what I've heard about the Lords of Shadow games, I wouldn't be surprised if my least favorite would be from one of them, but I have just about zero interest in ever playing those games, so I can't comment on what I haven't listened to.
So from what I have played, maybe I'd go with Door of Holy Spirits from the Reverse Colosseum in SotN? It's an amazing soundtrack overall, yes, but I've always found that particular track jarring and unpleasant to listen to. It sounds like something out of a slasher film, and while, sure, Castlevania can be considered horror too, it's just not the kind of atmosphere I expect in a Castlevania.