A-Pick any one .416 cal cartridge - .416 Remington Magnum

B-State why you would pick this cartridge over the others.
-My retirement years will include a lot of traveling hunts, including a couple to Africa. No other .416 (or .400 or .404) comes close to the availability of the .416 RM in places you might need one - Like Africa, Australia, or Alaska. Even the .416 Rigby is a far distant 2nd place. Loose your luggage with your ammo on your way to Africa and with any of the others you are probably SOL.

C-What type of gun would you purchase or chamber it in. Blaser R93 Professional

From what I've heard and read, any .416 that can muster anywhere above 2150 is good to go and exceeding 2500 can hurt penetration due to bullet problems. So the Taylor, or even the old .450-.400 are fine performance wise. The Ruger looks like a good, well thought out design and the .400 H&H is decidedly better is every detail than any other I've seen.

But the .416 Rem. has no issues, having enough case taper for the pressure it runs to assure reliable extraction in any properly built and maintained rifle in any ambient temperatures you'll ever encounter.

The .30-.338 magnum and the .308 Norma Magnum are both better cartridge designs than the .300 Win Mag. But I would have no problem finding some .300 Win Mag in Jo'berg. Not so the other two.

Unless you never hunt more than 30 minutes from your reloading bench, always pick the most widely available cartridge in a given class.