I've had the best luck with the .243 Winchester by far. Bang flop gun of doom
Followed by the 22-250 as a close second.
If you handload, a loaded down 270 works nice /ubbthreads/images/graemlins/wink.gif
The 223 will get the job done without too much fuss, but its borderline for quick consistant kills. Tough knocking them down when animal is quartering to you, as is typical of a called in dog. I find most of them though /ubbthreads/images/graemlins/wink.gif
221 fireball bears mentioning if you hunt in open terrain, have small yotes, and can wait for a picture perfect shot. I've used the Fireball on my limited amount of "field hunts" here in the East with good results.
I've killed coyotes but don't recommend them for "go to" guns with 30-30, 30 06, 44 mag, 357 mag, 22 mag, 22lr, 22 Hornet, 12 gauge, and a few I've forgotten.
If you search out a consistant killer when things don't go just so, pick a 243. Next 22-250.
I guess terrain and hunting styles are the biggest factors in picking a gun type and caliber for your needs though. My choices are based on Eastern calling set-ups, and I know things are different elsewhere.
Good hunting, Sleddogg