Driving dynamics with a competently comfortable interior (Stelvio) vs. Interior luxury with competent driving dynamics (GLC).
Decide which mix you prefer.
Fun with some lux, or lux with some fun(so long as everything works in both cases, although the Stelvio will drive nice so long as it is not on limp mode. The GLC requires alot more computer intervention to control it's weight and deliver dynamics which leaves more room for failures affecting the drive.
They both use Magneti Marelli and Magna international (Magna spun out of Daimler-Benz and is the designer/builder of the G wagon) and Bosch for the majority of thier electronic supply chain so despite what fanboys/magazines say the reliability is about the same, although MBZ has a better dealer network simply because it is larger and more established.
Great cars but the looks of a Merc haven't been doing it for me for years, I dunno. I think they need to reach back to their roots and come up with some new sort of retro/modern look. Not that BMW/Audi has it nailed either but they look better. I think Alfa has done a nice job of the retro/modern look. If the Tonale is any indication of what's to come on the coupe and mid-life changes, we're in for a wild ride.