I use a couple different ones.
The first is a 222 Remington, with a 50gr Sierra. It's murderously wicked on furry critters out to about 250. Possibly my favorite rifle cartridge of all time.
The second is a recent addition. I just finished a Savage 110E build in 243 Winchester. So far, I've used 60gr Sierras and 85gr Speers. Both are boringly accurate, but I've not yet seen how the Speer performs against a live target. The Sierra load turns coyotes off, that simple.
Third, and final, is the good old 30-30. I load a 110 grain Hornady, that will absolutely stomp a varmint as far as iron sights can see. Or at least as far as I can use them. The result is, well, wicked. It is almost too heavy for a varmint load to be honest.
Mac