Modern varmint rifle caliber

[brybenn]

With the right bullets either of the list will work well. Personally id go 223 from your list with a fast twist barrel

I love the 25 caliber so im building 2 different 250 savages. One for varmints crows to coyotes and the other for coyote wolf and deer. After i finish those ill likely build a 223 for plinking

 

[grelmar]

.220 Swift

But in the real world...

.223/5.56

It's effective, and there's a VAST array of readily available commercial ammo, so it's easy to find something that works great with your gun out of the box. Also, cheap bulk ammo is available for high volume varminting.