Infotainment is a common cool factor. Both the CLA and A3 have advanced connectivity and entertainment systems packed with features. We'd place Audi's MMI system ahead of the CLA interface. The Audi system tucks smoothly inside the dash when the vehicle is parked (in the CLA it's fixed), and MMI includes stunning Google Earth and Street View maps, fed by a high-speed 4G LTE embedded data connection that you can share with your passengers and their devices.
The Mercedes CLA includes more standard safety features, though; radar-based Collision Prevention Assist is included, as is the Attention Assist system that helps prevent drowsy driving. Active-safety options in the Audi include blind-spot monitors and adaptive cruise control.
Outside of MMI, the A3 doesn't have many features, trims, or special materials to get excited about. It feels like a (VW) small car that's been dressed up for the task of Audi duty; on the other hand, the CLA feels finely detailed, as if the company tried to give this car some of the cues, as well as the ambiance of M-B's larger cars—as well as a few of its own.
The A3 outpoints the CLA 7.3 to 6.6 here for a couple reasons. First, the Audi has crash data, and it's very good. Second, the Audi has better standard features. While we'd argue that the Benz may look like a better luxury car, the Audi is a better "car" car. We'd pick the Benz for a ride to the valet lot, but the A3 for most other circumstances.