Ditto skiinewmexico and Shawnee;
I've killed several hundred deer with a .223, not to mention the .22Hornet, and recently the .22-250.
For the single best factory load, I'd recommend the Winchester 64gr PowerPoint, though I haven't ever used it. I have however used the 60gr Hornady PtSpt,(This would be my first choice if Hornady offers it) and the 63gr Sierra as well as the newer 65gr GameKing BoatTail Spt. (I've only taken one deer with a factory .223 load, and I wouldn't recommend it. -(Remington 50gr PowerLokt Hollow Point. after 5 hits, it took a .357mag round to the head to terminate the deer, bullets penetrated only about 2-3", and two to the neck failed to break the spine.....Very accurate small varmint load, however. Range was actually too close ~45yds.) This however was my only failure with a .223.(though the deer still died, eventually). An envyable record.
The most deer have been taken with the Hornady 55gr PtSpt (The bulk ones, with a cannulure). Simply due to the fact that they are cheap (or were, the last 1,000 I bought in 1999 for #42.00/1000). A friend uses about 100 per year. He uses them in a T/C Texas carbine w/16.5"bbl. He's taken them out to 325yds. He uses a shoulder/spine shot usually, however I've seen some with gut-shots that went less than 50yds. (He's got a large farm and takes them on crop-damage permits. I used to issue him his permits, and occasionally accompanied him.)
Simply put, a well placed .223 Soft Point (don't even bother with the Ballistic Tips, V-max's, or various hollow-points) of 55grs or heavier.
A heart shot, or a shoulder/spine shot is the most reliable. Neck and head shots are difficult, especially for an excited neophyte, so avoid those. With broadside hits, I usually get complete penetration and good blood trails. Essentially indistinguishable from the .243wcf.
However, when hunting "horns", I usually defer to a larger rifle, such as the 7mm08, .257Roberts, or if really long shots in really windy weather I'll blast them with a .257WbyMag, or, for deer jelly, the .300RUM. But, this year opening day found me with my wee little Rem. Mod-7 and some 60gr Hornady SoftPoints. No deer, but did whack one coyote!