For me, probably Pyramid Head, because he seems to just embody sin and fear in general. More specific to me would be something to do with lust, I guess, or more likely something embodying my crippling fear of rejection. Maybe a phantom of some sort that can shapeshift into whatever I'm most afraid of at the time, though the worst would be a form that could try and seduce me then kill me (or simulate killing me) right at the moment of seduction. Or something like that. I don't really know what monster I'd end up with, so best to say Pyramid Head and be done with it.