See the Truth -- 1U
Look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in a any order. If you cast this spell from anywhere other than your hand, instead put all those cards into your hand.
How good does a 1U cantrip need to be to see play in Vintage? Telling Time is unplayable but it's not farfetched to imagine casting this thing easily and often with Snapcaster Mage, baby Jace, Underworld Breach, etc. (Of course Brain Freeze is much better once Breach is in play, but See the Truth both helps you find the Breach and then has a massive payoff once you land it.)