Which artifacts are best to equip a hero with?

Some books offer good protection, but you only get 1-2, and that's it. By the way, take a look at your hero at the end of a long scenario; he's dressed LIKE A CLOWN! Power helmet, Amulet of Life, regeneration armor, Boots of Lava, a cloak with stars, and also a book and a maul, and a bow on his back.

Any will do. The main thing is that the hero knows this magic. In general, mixed sets are the best (Traveler's Book, Apprentice's Book, Adept's Book, Archmage's Book, Guild Compendium, Demonology). Or, instead of a book, you can use a staff. That's also a decent alternative. For example, the Summoning Staff enhances summoning (it seems to be by 15%, but correct me if I'm wrong).