An article in a recent issue of The Horse magazine reports the latest research. Zebra-striped fly sheets work the best. They confuse the flies.
I have also been looking at the zebra patterns. In more careful review my top three now our premier equine super lite https://www.premierequine.co.uk/products/super-lite-fly-rug-with-surcingles
Amigo https://picovs.ca/products/amigo-camofly-fly-sheet. They are not pretty but I like the low neck like. I really like the disk closure on these. My only hesitation is I had one years ago and I just thought it was a bit tight in his shoulders. This was like 10 years ago so it may not be the same today.
The Weatherbeeta combo I kick myself for not buying last year when it was on sale super cheap