I have read the Recombetek (sp?) is the best, however, my vet practice uses the Fort Dodge combo vaccine (WNV +EWT), which is also what I order myself and give. I've used Fort Dodge combo since it came out, and the non-combo one prior, without any issues. I like it because I've had no reactions and it cuts down on the number of shots I have to give... horses that don't "go" anywhere just get that combo + rabies.