Pick a call, any call, they all will work. True some might work better than others, but they all can be effective. Also, don't forget about the no frilles call that you have with you every where you go, your own two lips. If you have a coyote within your eye sight, simply use your lips to makes some squeeks, that alone will often bring them in closer. Try not to over call, coyotes are very good about pin pointing the source of sound, and with the bow, you need them to be unaware of your location. They won't stand around and look at you long if they see you drawing, so draw when you can't see thier eyes!
Good luck. Calling a coyote in is one thing, killing it with a bow after you get it called in is another. It can be done, be there and done it several times!