Any standard cartridge of .25-cal or greater from the .308, .30-06, 7x57 or .284 class will do anything you would ever need for whitetails.

On the extreme outside would be rounds like the 7mm Rem Mag, the .270 and 7mm Wby Mags and the SAUMs/WSMs. Cartridges like the Ultra Mags and STW are way more than needed and can only be effectively used by about 1% of the hunters out there, and even at that for only about 1% of their shots at game. That is an awful small percentage of actual need to take that much abuse at the range.

If I had to choose, I' d go with the .284 Win or the now commercial 6.5 x.284. Both will take whitetails cleanly at 50 or 500+ yards and are equally lethal at at either range.