Let me try a long answer to your short but good question.
It's my wife's car, and it's brand new, but I have some thoughts.
The MDX AWD and our GLA 250 FWD are VERY different cars, apples and oranges. In actuality, the the GLA has more in common with my loaded 2015 Cherokee Limited.
Our Acura MDX was three and half years old with 38,000 miles on it. We got it for a bargain price because the model was just about to change substantially and it didn't have the tech package --- no nav, for example. It was a $40,000 plus car that we bought new for just over $35,000. We traded it in and got about $25,000 for it, a great deal based on the use we had gotten out of it and what we paid originally. AND we got a great deal on our new GLA, almost $4,000 off MSRP based, I think, on the facts that: it was the last new 2015 at the dealer, it is FWD and not AWD (4Matic), and it is a color that a fair number of people don't care for - Universe Blue, which we love.
Now the car to car comparison with the MDX:
Our MDX was primitive techwise as compared with our GLA, which has nav, blind spot monitor, etc.
The MDX feels/drives like a luxury SUV. The GLA feels/drives live a combination small sports car/sport wagon. It's a buzzy 4 cyl. that is fun to drive.
I just said that the MDX was a luxury SUV. Our GLA really feels like a luxury car apart from the small buzzy engine. The interior from the steering wheel on up feels and looks luxurious.
I am an old guy, not very bendable, and our MDX was very tough to get into --- the pillar for the windshield angle and where it met the roof line always seemed to get in the way of my head climbing in. The smaller Mercedes is much easier. (Although not the AMG version that I climbed into at the dealer; that was really a struggle to get into and out of -- something about the seats).
Lastly, I remain interested in getting an answer to my question about the contents of my GLA trunk. Is it really only supposed to have tow hook and a long rod in it? And what is that long rod? Thanks.