There's no best cartridge for whitetail.
Only favorite cartridges for whitetail, under "X" conditions.
Very true. I don't use the same rifle in the same caliber that I employ in central or Eastern Washington (rolling plains, highlands) when I go back and hunt family land (lots of thick forest and swampland) in Upper Michigan. We can argue ballistics performance 'til the cows come home, but at the end of the day, what's best for me is what I shoot best for the type of hunting I'm doing, the terrain, forest, grasslands/farmland, the distances for shots...
I'm perfectly happy, performance-wise, with .243, .270, .30-06 and 7mm Rem Mag, perhaps only because I never hunted with any of the trendy calibers but grew up hunting whitetail in Northern Michigan with a lever-action .30-30 that worked fine back then. My old partner swears 6.5 Swede is the best ever, but the younger guys I work with all talk up 6.5 CM and 6.5 PRC. But, I vote .30-06 for its versatility.
Anyway, didn't Jack O'Connor settle this once and for all back in the '70s when he actually conceded that .30-06 was a lot more versatile caliber than his favorite .270?