For a mage, which amulet/necklace is the best choice? Necromancer's amulet gives you +50 magicka and 25% reduction for Conjuration cost, but at the price of 75% reduced health and stamina regen. The tradeoff seems okay for a straight spellslinger.

The Gaulder Amulet give +30 to each attribute, which is nice.

Savos Aren's amulet gives +50 magicka also.

Thoughts? Any other options? I'm not counting enchanting at the moment.

As far as unique items go, yes, it's arguably the best, but only if you're heavy into conjuration. Depending on your level, you can find better necklaces.