In 3-2-1 order, Id likely choose Belakor, the Dark Master
Tons of commanders synergize with artifacts, some of which are artifacts themselves and feature somewhere on this list
Because your guys all have lifelink, you gain a lot of extra life this way even if they are blocked
Note that he can target himself to draw two cards and leave a blinkable body behind
Getting Sneezy into play early will help you make favorable trades early on an establish a board
Urza's Command can drop the power of other player's dorks out of nowhere, make a Powerstone, make a tapped Construct token to win the game, and then scry and draw, so I think that the Construct and scry and card draw are the default here, and that's pretty good for four mana instant speed