I happened to live in Orlando and we got an Infinity and a MB dealership side by side here by Millenia Mall, and I test drove both vehicles within hour of each other. Both vehicles were FWD, i.e. QX30 and GLA250 SUV. QX30 interior is very luxurious and loaded with finest wood veneers and details, but it was very very cramped. Head room was limited, especially in the rear. The ride was more supple but it was mushy when your corner it hard. It was slow, almost like Lexus (refrigerator on wheels). GLA250SUV's interior on other hand was spartan, not luxurious to the level of QX30. The metal dashboard trim was industrial looking and coarse. The ride was firmer, I would not say harsher; the suspension was more compliant in absorbing bumps. It felt more rubbery and "velvety". The GLA handled the corners with much more finesses, the turning radius seemed to be tighter and steering was more precise, perhaps due to tighter suspension. The GLA's acceleration was definitely faster than QX30. These of course are my personal observations, and I am by no means a professional auto reviewer. After test driving both models, I am opting for GLA250SUV.
By the way both vehicles do not come equipped with neither LED nor HID headlights as standard equipment. In GLA250 SUV it is available as Option 614, which is impossible to get, unless you place a order for it.