Why would you limit your horse'a hearing capacity?
Highly recommend De La Coeur. Although they can be pricey, they are easily customizable and absolutely gorgeous. The thicker lining in the ears works well to block noise although the ear blocks work better than any bonnet. At least in my opinion :)
One of my horses seriously objects to the idea of things going into her ears, but is very noise reactive. Long-term I'm hoping to warm her up to the idea of the pomms, but for now at least, I am using a Schockemohle bonnet that definitely helps. The effect is not nearly as good as pomms would be, but it is definitely better than nothing :)
I have one De La Coeur, I can't comment on how well it works vs. plugs, but the bonnets were all gorgeous and so well made. The noise reduction version had thicker material lining the ears, almost like foam. They were very easy to work with for customization :)