I'm obsessed with the Mazda's look, and the interior is amazing. I love the Audi's interior too, and it looks good from the outside (nothing special though, but it's a good look that will still look good years on).
Mazda comes with everything, blind spot monitor, full bose audio, rear camera and park distance, many safety features, etc.
But, the Audi's infotainment seems really nice. It's a bit of a gamble with the features on the Audis as there are so many options possible.
I was set on the Mazda, but I realised that it's possible to get a newish A3 for a similar price.