You have gotten some great advice already. Here's my $.02. If you expect to be hunting deer in a "shotgun only" area, consider buying a quality pump or auto loader, and 2 barrels. One rifled for use with sabot-slugs, and one that accepts choke tubes, which most do these days. By doing so, you will have a combo that should be accurate enough with the sabots to take deer cleanly out to 100-125 yards or so. With a set of choke tubes, say a "full" , a "modified", an "improved cyl", and a "turkey choke". You would then be good to go fro anything from turkeys to ducks to rabbits to dove, etc. If however you will be hunting where a centerfire rifle is OK, I am a big fan of the 30 caliber hunting rounds. My favorites is the 308 Win. However for one gun, I'd go with a 30.06 Spr. I prefer a bolt action because generally speaking this action groups great and at least gives the hunter an opportunity for a relatively quick follow up shot. Nothng wrong with a 270 Win., 243 Win. , 30-30 Win., etc. ... however I personally would not use anything smaller than a 243 Win. on deer sized game.