I agree with bugel' s selection. Asking for one cow call is like asking for one golf club. You need more than one for different situations. My calls are:

Hoochie mama - sqeeze call. Can sound like a herd with another call in your mouth

Two diaphram calls - These allow you to be at full draw or shooting position and give a cow call to stop a bull.

Reed call - Reed calls make great estrus sounds and are just a real good cow sound. Probably my favorite if I had to pick only one and they' re real loud.

I think you need all these different types in your arsenal. If you don' t you' ll get in a situation and wish you had em.