I'm currently writing this from the Maritim Düsseldorf Airport, which I can highly recommend. This is my first stay here, usually I have been staying at the Sheraton which has kind of underwhelmed me every time that I stayed there (esp. in terms of price/value ratio). While the rooms at the Sheraton are quite small and a bit weird (due to their wedged layout caused by the building's structure) the rooms here are almost twice the size and the hotel is a lot more modern than the Sheraton.

Rates for both hotels are roughly the same, so I'd recommend you try out the Maritim next time you'll have a layover in DUS. Among other things, the hotel also features a nice wellness area with a (really) small pool and a nice sauna (both not present at the Sheraton). The downside is that Maritim is an independent hotel chain that doesn't really have a loyalty scheme, so it's a bit hard to get a real bargain (or upgrades etc.) - however, I'd say that it's really worh it, nevertheless.