Best Fly Spray for Horses?

I use NETTEX Fly Repellent (Advanced Formula) It lasts on the coat for up to 72 hours and helps soothe insect bites as well as repel flys and insects. It's the UK's No. 1 brand but don't know if you could get it in the US, another is Naf Off from Naf, again i don't know if you could get it.