Forget the very long range stuff for now. If you're asking which caliber would be best for you for shooting deer and coyotes I'd suggest the .243 as my personal choice. Either one can be very accurate and both are capable of making clean, humane kills on the game animals you mention. My reason for suggesting the 243 is simply that it has less recoil which may help a newer rifle shooter and it is very flat shooting at all reasonable distances (but so is the 308 actually). I've been deer hunting for fifty-three years and I have yet to ever even get a shot beyond two hundred yards at a deer...and I've shot a LOT of deer. Yes, you can get shots longer but it doesn't happen very often. At least not in the North East US. Not to bash Mossberg even a little bit but if I were actually looking for a rifle to shoot at very long ranges with, that wouldn't be my first choice of gun to get. In fact, it wouldn't even be on the list of guns to get. It's a very adequate gun for deer hunting but for six hundred yards and beyond it's just not made for the task. Again, concentrate on closer distances. Up to even three hundred yards both calibers will be more than flat enough shooting and each will kill deer. At longer distances the 308 with heavier bullets will have more retained energy and might be a better choice.