My
favorite would be a good autoloader in something a bit stouter than a 223, be it a 6.8 or .308. Honestly, any decent deer rifle will work fine in most situations during the daylight hours and I've killed more with bolt guns than anything else.. I've occasionally run across groups where I was able to connect with multiples in one "volley", and the semi-auto was handy then. I've also lined up a few to try to make the most of shot #1, and you can do that with whatever type of rifle you have in your hands. If I'm reaching for a sure 'nuff PIG GUN, it'll be an AR10 in .308win.
Sometimes they are just stupid and keep popping out of the woods to get shot. You can use whatever you like when you are one-at-a-time'n them. I've shot 4 before in one spot with a single-shot rifle in the same evening.