I myself have a blue Caseformers for my 950XL, and it has been good no complaints from me, but if you're looking for aluminum cases here's a listing I saw on ebay a few days back, maybe check it out and see what you think. Hopefully it helps and good luck.
It's tough and seems to protect the phone well. Only thing I don't like is that the buttons are stiff. When I try to press the power button I end up pressing both the power and volume buttons causing it to take screenshots or open the feedback app.
PDair has several "leather" cases for the 950XL.
Excellent quality, lasted more than 2 years on another device. (I had the "Flip" style)
Padded enough that it plopped on the floor gently.
$40 +, Looks like a 10% off sale now. https://www.pdair.com/microsoft-lumia-950-xl-case
I don't think you will find anything better than the plastic cases everyone has been recommending. I've been searching for the ultimate best case and I still haven't found anything worthwhile that I would consider to be of "High Quality."