All I can speak of is what I want or need in a dog, from what I do for a living. Excuse my rambling, as I'm just throwing this off the top of my head, in no specific order or such.
There really isn't too many right or wrong answers on this topic. One could take their wife's prized miniature poodle or yappy silky terrier and use them as a decoy dog. The essence is a dog that will take the focus off of the caller and put it on the dog. It could be a yappy lapdog that is picked up from the pound or a 90+ lb catahoula that one uses. It really doesn't matter, as long as it helps put fur on the ground. That being said, here is what I look for:
I prefer a dog that is tall enough to see over the grass in a variety of calling terrain, but not so big as to intimidate a coyote. I like that 45lb range with good legs, light on their feet, grit, super friendly personality, and most importantly, intelligence.
Color really doesn't mean much to me, but I do prefer a short coat, based on where I live and the temps. I don't know if a coyote looks at a dog as a "dog" or another coyote...and actually don't care. I've called a bunch of areas that I can guarantee the coyotes have never seen a farm dog before. I've witnessed their interaction and behavior with other coyotes and dogs, and it's pretty much the same behavior. A dog needs to have that aggressive/passive behavior to effectively play the cat/mouse game needed. On at least 6 occasions, I've had my dogs kick up a jackrabbit while walking to a stand. Off they go, only to beep them back and have a coyote in tow. Each time, the coyote was more curious than anything, but died still the same, without a single call being blown.
I prefer a dog that works close, well within gun range. Our average shot coyote is 40-50 yards. I want my dog within that range, unless casted out by command. We call for both coyotes and bobcat and I don't want a dog that will scare off a prized cat. A dog must sit tight and not engage until given the queue, either gunshot or voice command. If a coyote is coming into the call, I absolutely do not want the dog to engage, but if he's heading out, I expect him to go get him and attempt to work him back. When calling, everyone on stand works as a team. I expect a dog to be fully alert on stand and watching for game. I have no patience for slackers on stand...including dogs.
I don't need a cold nose on a dog, but a hotnose for running a track, especially baying up wounded game. I prefer a silent runner, but once bayed, expect a good mouth to alert to their location. I want a dog to stay on bay until we arrive or give the command to come back. When it comes to stopping runners, I expect a dog to fully engage and hold a coyote. The last thing I want to do is walk miles after a wounded coyote...especially at night.
I don't want a dog that has too much grit. I've had coyotes bug out at the sight of a dog charging after them, while they were coming into the call. That being said, I don't want a sissy dog either. If they must fight, I want them experienced enough to do it right and not get bit up. They need to be able to handle their own if engaged by multiple coyotes. I've watched my dogs handle upward to 7 coyotes trying to catch them. They need to be smart enough to know when to push a coyote and when to pull back and let the gun take over.
I prefer to run 1 dog most of the time and 2 during the spring or breeding season. I prefer to run 2 dogs at night, as well, due to rough bay-ups and not getting suckered by a partnering coyote in the dark. Plus, I hate walking miles after a coyote that bays, then bolts when we approach with the headlamp, only to be bayed up again in 1/2 mile more.
Also, I want a dog to be a true hunting companion. If we are hunting coyotes, bobcat, badger, raccoons, hogs, quail, dove, etc... Of course, they must be stock proof and flat ignore cattle, horses, sheep, goats, chickens, etc...
Gunner gets the most exposure of my dogs, as he is what I use with most my clients. He works out well for guiding hunters. He gets along with everyone, has great truck manners, superb stand discipline, stays out of the way of the gun, doesn't spook coyotes anytime of the year, tolls when needed, and recovers game very well. He does very well for what I do for a living. No dog is perfect, just as no man is. You find its strengths and leverage them to your advantage to put more fur on the back of the hunting rig. I do have and use other dogs, based on what I need at the time.
Dixie, my jagd/cur cross that I bought from Devin, tolls very well for her young age. She's a bit too aggressive and has scared off her share of coyotes, but I think I can pull that back with training and maturity. I only use her for springtime and/or breeding season and sometimes as a helper dog on nighttime recovery. With time, she will be one heck of a good dog, doing everything I have Gunner doing and then some.
Mattie is my pitbull. I don't consider her a decoy dog, nor label her it. She was purchased as a pup for the sole purpose of being a brood biitch. But, I have found that she makes one heck of a good nighttime recovery dog, especially for runners. I use her at night, when I have room in the hunting rig.
Everyone had different ideas and tastes, based off of their expectations and the way that they hunt. These are my ideas on what works for me and my hunting/calling style.
Great topic man!
Tony