Spidey - Easy. Your opponent is playing a red speed deck. Seeing that you're playing mana acceleration in the form of artifacts, he boards in Meltdown on Game 2. You have either Sol Ring or Sisay's Ring in play. Which one is he more likely to be able to blow up?
Or how about this? Your opponent is playing burn, and has no creatures in play. He's at 3, you're at 1, and you have no access to countermagic. You have Sisay's/Sol Ring on the board. Casting Peek lets you see the Volcanic Hammer in his hand, and you draw Animate Artifact. Which would you rather cast it on?
Or how about this? You have Pyromancy in play, and are stuck at 3 land. Your opponent is about to smash your head in with a series of fatties, but is at 4 life due to you activating Pyromancy at every opportunity. You have no cards in your hand, with Sisay's/Sol Ring in play. You draw, and it's not a Fireball, but it IS a Boomerang. Which Ring would you rather bounce and club your opponent with?