I'm not a hunter. I was trained as a sniper. Said that, most deers weight about the same as most adult humans so what works for one should work for the other one. It is true that deer have more density, however most humans don't walk around naked so taking into consideration clothing they are pretty compatible.
One-shot-one-kill. Shot placement is essential, deers or humans. If you don't care about preserving the head, then head shot is master, otherwise hit the heart. All other places won't get you a clean kill.
Practice, practice, practice till you can place a bullet between 3" at any distance you are to take the shot, otherwise practice more or pick up a different hobby!
When it comes to choosing a cartridge, there are aways two things to keep in mind: The weight of the target and the distance where the target is.
Up to 500 yards a .243 w 100 gr. will do the job just fine giving you superb ballistic thanks to its flat trajectory. The .243 will work equally well for the humans and deers.
The .223 r is a varmint caliber and should not be used for humans or deers. I had my share of arguments while in the service due to the 5.56 NATO and 9mm NATO (side arm) both wimpy choices for humans. I'd take .243 and .45ACP/.357 magnum thanks.
If you care to take a shot up to 800 yards, the almighty .308 w 168 gr. will serve you just fine. Bu realistically, how many hunters out there take shots that far? Again, I'm not a hunter.
As for the .300 w magnum 200 gr., that thing at 1000 yards has the same energy as a .44 magnum at point-blank! Unless your target is 500-1200 yards away NOBODY needs a .300 w magnum for humans or deers, if you think you do, you are kidding yourself!
So here is my 0.02, for deers and humans pick a .243 for short action or a .25-06 for long action, anything else is overkilled unless you constantly take shots over 500 yards.