Very interesting topic, although I do wish more posters would give the reasons for their selection.
Being that I already have the varmint calibers covered by .22 LR and 5.56, as well as a .308 for medium game, I would select either a 45-70 or a .375 H&H as my only Number 1.
I've been considering this for the past two years or so, and started out thinking I wanted the 45-70. After further research, and picking the brains of friends that have hunted the dark continent, as well as my aussie bride, I've settled on the .375 H&H as my only Ruger Number 1.
My reasons are manyfold. First, my other calibers can handle my other game taking duties well. Second, the ballistics of the round surpass, IMHO, the 45-70's rainbow trajectory. Third, ammo is available worldwide, and the caliber was even recommended to me by the Guide I was considering using for an Autralian hunt for Asiatic Buffalo. Fourth, it's a good caliber for moose, elk, and bear here in the states.
Most likely I'll have a Ruger Number 1 in .375 H&H later this year. Next year I'll probably do a Buffalo hunt here in the states as preperation for going to Australia for Buff and Boar.
Biker