RE: Most versatile
while i am partial to the 35 Whelen i'd also have to toss in the 350 Remington magnum. They are almost ballistically even. I'd even venture to say just buy a 300 or 338 RUM... not exactly practical for midwestern deer and such and maybe a bit hard on the shoulder, but i'd sure rather have too much firepower when i don't need it than not have enough when i do.
If you are a handloader then regular ole plain jane offerings become much much more attractive and versitile. If not then stick to a cartridge that is available over the shelf in a wide varity bullets choices, weights and velocities.
The Whelen (35 and 375), AI and non AI have been used for the biggest, toughest game on the face of the earth at one time or another. Tailor the bullet and the load to the situation and run with it. Ammunition is no where near as popular or available as many others out there though.
JMHI
Jamie