I have a friend who's staying in Grand Winston Den Haag (The Hague) in Rijswijk, and asked me about what to do in terms of air miles on his hotel stay. World Hotels don't have a loyalty programme…yet. They announced the launch of one in February this year but I still haven't seen anything being realised. But even still, I'll be the first to admit I don't know much about World Hotels since they have no presence in the UK…but it was remarkably simple to learn their details.
World Hotels have 25 airline partners, as listed on heir website. What's interesting about their partnership is that they only credit air miles per stay, and not per night like the other big hotel chains. So if you're staying more than 1 night in a particular location, unless you've got a compelling reason not to, then I would suggest staying in any of the other big brands.
For the European resident, I reckon the stand-out partner is Iberia, where you can get 1000 Avios points per stay. World Hotels even offer double and triple points per stay if you book on their special rates. You can then transfer your Avios from your Iberia account (sign up link here) to your British Airways account (sign up link here) freely and take advantage of the Reward Flight Saver redemptions which start at 2250 Avios points.
This is by far the most common type of air miles redemption I use, as it offers a massive discount on the intra-EU taxes.
World Hotels also earns miles on other commonly-used European programme like Flying Blue, Lufthansa Miles and More, and Millemiglia. But even with this is mind, I'd still put them to Iberia because you can use your miles sooner.