That could depend somewhat upon the kind of coyote hunting you do.

If you call them in, chances are that you'll eventually have one that you didn't see come in closer than you're comfortable with. In those cases, a lower power is a boon to finding them in the reticle quickly. Better yet, carry a shotgun too.

If you spot coyotes, or stumble on them while driving, you're probably going to want more glass.

Then, the matter of weight. I know lots of guys who buy a HB Varmint rifle with big glass and then slog along behind when we're covering ground on foot. For a truck gun? Maybe not such a bad deal.

My "position" prairie dog gun is a .22-250 topped by a 6.5-24x. No good for coyotes, unless they happen to be visiting the same prairie dog town that I'm sitting over. My coyote guns are a CZ527 varmint (with the micro-mauser action it feels about as heavy as my M700 BDL .30-06) with a 4.5-14x on top and a Ruger No 1-B in .243 with a 3-9x VX-II on it. Of the two, the Ruger's probably the most versatile, glass-wise. I don't know that I'd want much more more than the 4.5x on the bottom end for a coyote rifle if I'm calling them.

My recommendation? Go with a 3-9x if you intend to call or walk for coyotes. If your rifle stays in the truck and you're tending toward longer shots, consider 4-12x or something in the 4.5-14x or 6-18x range.

edit: Forgot to add, what kind of country do you hunt? Where I am out west, I can see coyotes about as far as my 60x spotting scope will let me. If you hunt back east, you're potentially going to need much lower powered glass than what I use or you'll find yourself looking at the veins in the leaves more than you will be the coyotes. Thicker the cover, the lower power the glass needs to be.