This topic is a huge can of worms but the caliber also depends on the skill of the hunter. I would use the largest caliber you are comfortable with in the .30 cal range. The reason is, a .243 etc is a capable gun in skilled hands but I have tracked many a deer shot in the shoulder with this caliber because it didn't do the trick. A .270 can also give a hunter false confidence, I've also tracked a lot of wounded deer shot with this caliber.
I recommend a .308 or a .30-06 at least. Once you become more skilled a smaller caliber is ok but the small calibers do not have the "knock down power" to correct an ill placed shot.

Ryan Campbell
http://www.hossfly.com