Racial ability: "Preparation".

To be honest, it's a strange question. I remember building and buying Angels in one of the games in the series. I just don't like the Tier 7 units in Heroes of Might and Magic V. Maybe it's a psychological factor. When a hero kills seven Giants with a single blow, making that heart-wrenching "krraaaag!" sound and breaking their skulls, it's unpleasant.
So, I prefer to focus on infantry. If I'm going to buy Tier 7 units, I'd rather get them from other castles.