I've palyed with the 243 quite abit starting about 1970. At that time I found it to be very unreliable on deer, but at that time it had more to do with bullet quality some would pencil through and some would break up on a rib bone so I pretty much shied away from it as a deer round. I should give it a chance again with premium bullets.
As a coyoter it has proven to be overkill for me as I hunt for pelts, again it had alot to do with bullet performance. I haven't tried the solid copper bullets YET, but have run some 62gr VGs and found them overly distuctive leaving softball sized exits. The new Nosler 55gr Lead Free Ballistic Tip is looking promising but they are so new that I have only killed two with them but both were devestating with small entraces and no exits and could take out bone.
I do my deer hunting with something larger as I like to see an good exit but most of my deer hunting is still hunting in heavy cover and I don't always have the perfect broadside shot. For my coyote hunting I like a light fast 224 that has proven qualities.
For me it's kind of like tools, a vise-grip will get it done most of the time but can make a mess of the job. I keep one in the tool box though. There is usually a 243 in the safe also.
AWS