Mercedes keeps the best price and it's not droppinng a lot by years. We bought our first Mercedes Actros in 2007 for 35 000 euros. At that time, it was one year old and had 200 000 kilometers recorded. Now, with 1 200 000 kilometers on itself, we get offers to sell it for 28 000 euros. And that's after seven years and million kilometers more. That's the same with every Mercedes truck here.... they keep the price high. On other hand, we had Renault Premum with Volvo engine inside. We got it for 32 000 euros back in 2009. One year after, it was 19 000 at market.
In EU you have Euro engine regulations. For example:
highway taxes for Euro 3, 4, 5 and 6 engines are not the same.
if a section of highway is, let's say, 10 euros for Euro 3, it will be 8 euros for euro 4, 6 euros for euro5 and 4 euros for euro 6.
Fuel economy plays roll there too. Euro 5 and 6 are consuming less fuel.
In our company we have Euro 5 and 6 engines but replacing older Euro 5 with Euro 6.
Euro 6 has cheapest road taxes against other Euro engines because it's more nature friendly. That forces us to buy them so we can get better profit per haul.