Just about any centerfire rifle cartridge is going to blow a coyote up (depending on the range). The smaller the hole the better (.17) and the less likely it is to overpenetrate (.22 mag, .221, .17) the better.

That being said: the .243 is the highest powered "varmint" cartrige out there. If your concerned about penetration, there are better choices IMO like the 223, 222, 22-250, etc.

The strength of the .243 comes from it's versatility and flat shooting. It's able to do everything from deer size down. If you want strictly coyotes I think a .22-250, .223, .204,.220 etc... woulddo better for you.