I chose the .375 H&H because it is the parent case for cartridges that are suitable for the widest range of animals/hunting conditions in North America. The small bore magnums, such as the excellent .264 Win. are slightly superior to anything else for really long range shooting of smaller game and the .338 Win. is as close to a truely "all-around" cartridge as we have for general B.C. conditions where Grizzlies are factored in. The .375 H&H it self, the .416 Rem. and the .458 Win. are very popular with the people in Alaska who deal with the huge bears there and, having been there, I am inclined to respect their opinion.
I don't care for the WSM or UM cartridges for several reasons related to magazine capacity and feeding issues and find that the '.06 based rounds are sometimes a bit less than I really feel comfortable with in remote, solo, backpack hunts in Grizzly territory. Actually, a .264, two .338s and a .416 Rem. would do me for absolutely everything anywhere I might hunt; but, I would probably need a .280 as well!