I like the big square wool coolers that come up to their ears. I’ve never bought one–my mother always won them in year-end awards, so we’d use them for all the horses.
Lucky me, my young horse is allergic to wool! He itches and rolls, desperate to get out of it. He got a Rambo fleece cooler for Christmas, and he really likes it. The fleece is THICK and SOFT, everything about it screams “durable” and “quality.” It’s kind of pricey, but it’s REALLY nice. Large fits my 16.1hh narrow OTTB gelding. If you have something taller or more substantial (like a big thick WB) go for XL.
The only downside is that it doesn’t cover their neck. It has belly straps unlike the big square wool coolers, so it has a snugger fit and dries the horse really fast. The big square coolers always seemed useless at getting belly sweat.