My thoughts on .375s doing what they're supposed to, the H&H wins for me, for pragmatic usage. The taper is a feeding and extraction benefit but it's the last 5% of the bell curve stuff, the .416 Rigby has a vaunted history and is shaped more like the Ruger. But it does feed slicker than any other round I've used, and I've used a few, I really enjoy working a well broken in .375 H&Hs bolt and chambering a round. That nose up tilt and taper scoots them into the dark hole like they jump in there.
Go to Africa and you can get ammunition with ease, yes, that applies to the minority of .375s but it's what they're meant to do. Your PH will have a dozen or more boxes of .375 H&H each missing four to twelve rounds left behind by previous clients. The H&H usually gains a round down in the magazine aside from in the Model 70, due to the taper. My RSM will fit five H&Hs down or four Rugers, I like the extra round. The Ruger is well designed but its claim to fame of fitting in a standard action also applies to the H&H, for whatever reason this is often conveniently ignored (Rem, Win, Zastava, Sako, and on put .375 H&Hs in standard actions from the factory).
Would I hunt with a Ruger? Absolutely! Biggest Grizzly bear I've guided was taken with one, backed up by my .375 H&H. And we all know Gate's long running amusement campaign is in jest and fun (well it appears some don't), and I'd miss it honestly if it stopped. Both are good, just ask yourself what you want from it, if you're never going to the dark parts of the dark continent it probably really doesn't matter. There's a far greater selection of factory .375 H&H rifles and ammunition, and can be found cheaper than the .375 Ruger offerings (Zastava). Ballistically they're twins, slight edge to the Ruger in standard action due to seating depth, in longer actions like the RSM the H&H equals or gains a slight edge. But if you put the Ruger in an H&H RSM / Magnum action (not possible without rebarreling and who would) it would gain a 30-100fps lead again.
Makers of .375 H&H and I'll be missing many of the more obscure and off continent makers,
-Federal
-Winchester
-Remington
-Dynamit Nobel
-Nosler
-PPU
-PVRI Partizan
-Hornady
-RWS
-Buffalo Bore
-Hendershot
-Custom Cartridge
-Barnes
-Armscor
-Kynoch
-Choice Ammunition
-Hunter
-DoubleTap
-....More, African, Australian loadings etc excluded.
.375 Ruger
-Hornady
-Maybe a couple of the boutique makers? Couldn't find it on Buffalo Bore.