Actually, and perhaps unsurprisingly, both of them hold on to similar amounts of value. Both were more or less the same price when new and both are now worth between €15-18k depending on the model and history. 

 

As they age though, I'd expect the Kia to hold on to a fraction more value than the ix35, simply because the Hyundai will run out of original factory warranty two years before the Sportage does. 

 

In qualitative terms, there's little to separate the two as they're mechanically identical. Both are spacious, comfy and nice to drive so it comes down to which one your prefer the style of and which one you can get the best deal on.