I've used a handful of AR's over the years for predators and have loved them all. Just about any AR set up to your preferences will be an excellent choice for fox and coyotes. Here's a few options I prefer on my coyote AR:
-free floated handguard
-direct impingement for weight/cost/accuracy edge
-quick detach sockets on stock and handguard for QD sling
-16" barrel of a medium weight, (not light or bull)
-improved trigger- most entry level triggers are not ideal for accuracy, I really like the RRA 2 stage
- 5.56 or wylde chambering (just cause I like options)
-Forward assist (to help close that bolt a little more quietly)
-Dust cover (mostly to keep out the snow in bad weather as I have had actions ice up pretty bad before)
I have run DPMS, Bushmaster, Colt, Remington, Olympic, Rock River, and recently Troy AR's (all in 223/5.56). All have been very accurate, reliable, and effective and I can recommend any of them. Good luck and let us know what you choose!