There's probably not a predator call on the market that won't call in a coyote, if used correctly. I'd suggest picking up a closed reed cottaintail and/or a jack rabbit distress call. Both will work in most places, even if there aren't any rabbits around. I prefer open reed calls because of the diverse sounds that one can get out of them, but that is just a preference. Set up where you can see down wind well for the approaching coyotes, they almost always come into your downwind side.
When you call a coyote in and kill it, you can sometimes keep calling and another may show up, but there is no need to stay for over 30 minutes at that one spot. And, if you kill one/two at a spot, give it a week or so before trying that exact spot again. In general, you need to move at least 1/4 mile from each spot for your next set, in wide open country like out here west, we may move a mile between sets. Amount of wind and cover are decideing factors on distance between sets, as heavy cover/wind both keep the sound from traveling a great distance.
You may find that calling them in is one thing, but getting them killed is another. Good Luck!