Man, it's hard to participate in a thread where Gatehouse is reasonable!

A new paradigm!
But I'll try.
If you enjoy the nostalgia aspect, the H&H is the only possible choice. If you are the sort of guy to whom "new & improved" is a mantra, and "NEW" a religion, maybe the Ruger is your baby. But, honestly, it seems as though the choice of rifle should come first, and then the logical cartridge choice for that rifle would follow. If you are looking at a Win70, Sako, CZ, Rem700 etc. you have the room for the H&H, so why not get it? One of my pet (and largely irrational) peeves is short cartridges in long actions...a .308 in a Tikka, or worse yet a Ruger #1, just rubs me the wrong way.
On another practical note, .375H&H's tend to be a bit harder to find simply because people cherish them and hang on to them, whereas .375Rugers come up for sale constantly, because...well...you know...