1. The sniper's bow can be replaced with a golden one (without a penalty to range) and still retain 2 additional slots.
2. The Admiral's Hat. If there's no sea, it's a useless artifact. Extremely useful on sea maps.
3. The Horn of Plenty. If you have enough resources, you can do without it.
4. The Ring of the Mage. This artifact is only good for a Barbarian who has problems with magic. With at least 12 magic skill, it just takes up space.
The remaining artifacts are great and among the best.