This could be exactly like the perfect deer caliber......
There isnt one. What do you consider varmints? If they include predators, do you want the hides? How are you hunting? How long are your shots? Do you want red mist? Do you reload? How much do you want to spend?
On and on and on and on the questions could go.
There is no perfect varmint gun. But, if you want one that is middle of the road. Can be loaded to hunt most varmints and predators for either red mist or lower hide damage. Can be loaded to shoot very well out to 300 yards or further with the right load and person. Cheapest to shoot in most cases, whether you reload or not. It would have to be, yep, you guessed it. The .223.
Yes other guns will outshoot it in distance. Others do better on hides. Others do better on red mist. But for all around, its pretty good at everything.
Kinda like a Yugo. (or a .270)
Andy