The best artifacts in the game

[masotime]

For me personally, I find that I can't do without the artifacts below.

Robe of Sar Issus (1/2 cost on all spells) - given how difficult it is to regenerate mana now (the dragon wells are the only way to get to full, and that's only once a week), I find it invaluable to have this robe on any Magic hero. Sadly, might heroes can't use this robe.

Boots of the Wayfarer (+8 movement) - kind of a no brainer, but the extra movement makes a huge difference when gathering mines and resources, and chasing that annoying enemy hero.

Ring of Haste (+10 to initiative) - In a turn based game like Heroes, striking first makes all the difference. Not only that, your hero gets to use spells and abilities before the enemy hero does. With the nerf to mass haste, passives like this artifact and from the Ambush skill are invaluable.

Unicorn Horn Bow / Emerald Yumi Bow (no range penalty / obstacle penalty) - This affects the output of ranged units so much it's not funny. While the Emerald Yumi bow should technically be superior to the Unicorn Horn Bow on all counts, a bug currently means that all half-range units only gain the benefit from the Unicorn Horn Bow, and given that the benefit is effectively 2x damage for a ranged unit, it's a very big deal.

What are your favorite artifacts / artifact sets?

[RollingWave]

The Guardian Brestplate's ability to negate the first 3 strike is crazy.

[Naki]

The Shackles of no Retreat are useful.

[maltz]

Shadow Comb - 1 Puppet Master per battle, useful for heroes who can't cast dark magic. Against the toughest optional battles this is the best shot - but PM frequently crashes the game.

Scroll of Mass Life Drain - again, useful for heroes who can't cast dark magic

[Macros the Black]

Shadow Comb - 1 Puppet Master per battle, useful for heroes who can't cast dark magic. Against the toughest optional battles this is the best shot - but PM frequently crashes the game.

I agree with this one. I played a game against my brother and attacked him in his town. His army had so many succubi I just would have lost if not for me Puppet Mastering them and slaughtering everything else he had (bonus points for him putting them in his tower first!).

[maltz]

Besides, the Comb can be worn by a low level hero. Same thing for artifacts that grants other spells.

[RollingWave]

True, Comb if gotten early would be uber imbal.