I don’t have a recommendation but I’d love to share with you what I’ve been told in the past:
First, shorter boots may be safer. If a tank of hot mash spills into your boots, the shorter they are, the less volume they’ll hold.
Second, and along the same lines, slip on boots may be a safer option (as long as they fit well) because they’re easier to get off in a hurry if something has spilled into your shoes.
I’d love to know what you wind up going with.