I voted 6mm and 22 cal.
I do most of my calling with an AR in 223. It's honestly more because I like the rifle than because I like 223, I prefer a little more speed. It's a tackdriver with 55gr V max reman ammo by RAM, and with 73gr ELDM Superformance loads. I wasn't overly impressed with the killing power on anything but broadside or head on shots with the 55gr V max load (only 2964fps). I like the 73gr ELDM (2750fps) better from my 20" AR. It exits, but puts yotes down faster.
My rifle is a DPMS Prairie Panther. It is one of the most accurate rifles I've ever fired with ammo it likes, ragged holes at 100 yards are common and a 1/2" group means I wasn't perfect. It has had the barrel lapped and an aftermarket trigger installed due to some early accuracy issues but has been great for years since. I'm planning to add a 45 degree mount and a small red dot now that night hunting is allowed. Not sure how much I'll use it but I think it will be handy to have at times.
I have a custom 243 by Flint Hills Gun Works that I really like for more open country. It is a Ruger M77 action, Pac Nor 23" barrel, Timney 2lb trigger, and McMillian Gamescout stock with a custom Kryptek pattern cerakote. It seems to shoot anything well, but I'm currently running Hornady Superformance ammo with a 58gr V max at 3823fps. I really like it for a truck gun too, no worry about range inside 300, just hold center and shoot.
Both rifles have Huskemaw scopes with yardage turrets if I need to dial for long shots. The AR has a 3-12x, the 243 a 4-16x.
I have a custom 204 I really like also. It's also a Ruger M77 with a 23" Pac Nor, Timney, and Boyds laminate thumbhole stock. I prefer the Hornady 45gr ammo in it. I had to many splash hits on shoulders or at close range with the 40gr V max Superformance or standard ammo. The 45gr is moving 3425fps and it often makes a tiny exit. I'll take that rather than a lost critter or giant entrance. It does not handle the wind as well as the other rifles so it gets used less. Calling where cats might show though I take it fairly often. It is a pleasure to shoot, like a 22 mag with an extra 300 yards of reach.
Past that I have a shotgun and 16" AR with a 1-4x Trijicon we sometimes use in tight spots. Generally though I like the reach of the other rifles. The reticle on the Trijicon covers most of a coyote's vitals at 200 yards and makes hits iffy. It's quick in closer though.