Big, hulking monsters are obviously a staple of fantasy gaming, but how different are they really from trolls or ogres? I mean the Chuul...does that even really belong in this list? It's more like a space alien than a hulk. I could reason having the Umber Hulk or the Grey Render(with a better name) and the Chull as distinct creatures, they obviously are. Significantly different designs, habitats, strategies, etc.... But the Umber Hulk and the Grey Render really seem like more or less the same thing, save one lives underground only.
Between the two, I find the mindset of the Grey Render more interesting, as everything the Umber Hulk does can be covered by the Grey Render...with an added touch of emotion and curiosity for players. Keep the Chuul as the massive underground monstrosity.