Ew Mercedes GLA250(2015) or an used Audi A7(2012 - 44k miles, with dealer warranty but not CPO)? Both priced at 40k?

I want to decide between a brand new Mercedes GLA 250 (2015) or a used Audi A7 (2012 with 44k miles on it. With dealer warranty but not CPO), both of which are priced at 40 grands. Test drove both, Mercedes was smooth and awesome. Audi A7 on the other hand was OMG! It had a WOW factor when I drove it, it was one of the best cars I've driven. More than that A7 is my dream car which I wanted to buy 5 years later. Now I am in a complete dilemma about which route to take. My friends ask to go for the new Merc. But my heart is not letting go of the A7 after seeing how good it is to drive it and it being my dream car. Please give me suggestions guys if you're good with cars. Am I putting myself at risk getting a used car for that kind of money. Would it cost me a lot to maintain a used A7? Which way should I go Merc or Audi? And which one would turn heads?