I'm totally going for the chrome girls.
I have no idea what the factory mud flaps even look like for the GLA, but have seen others that are painted to match the vehicle on the side not exposed to the wheel well and just assumed that Mercedes would go that route. I would never add them if they were just black rubber flaps.
I was considering them 1) so I don't have to perform as many evasive maneuvers and detours to avoid sprinkler runoff while driving around town, as I live in the middle of town and do very little highway driving except on weekends, so we're forever finding ourselves with a freshly washed car driving through sprinkler runoff and spotting up the sides of the car. That wouldn't happen or would be much less noticeable with mud flaps.
Also, I am getting a GLA 250 with 4MATIC for occasional light off-road use where mud flaps may save the sides of my car from some rock chips, etc.
If there were tastefully done (shaped and painted to match, rigid) mudflaps that worked with the sport package, I would certainly consider them because I'm much more concerned with preserving the finish of my car than what random people on the intertubes think about mudflaps. I will not, however, just throw generic floppy rubber mudflaps on it, so you can rest easily knowing that I hope.