Me! We have been to Hoog Vaals in Holland and Sonnenberg in Germany. Both are lovely. I always link to them on CP threads as i think the accommodation is much nicer - even the standard cottages. We had a Luxury cottage in Germany and it had a sauna, sunbed, fantastic shower, DW, washing machine/tumble drier. The food on site was good and reasonably priced.
We are going back to Hoog Vaals at Autumn halfterm - it's close to Maastricht, Aachen, Monschau, Valkenberg - all worth a visit - and about 3km from the Drielandenpunkt, where you can stand in Holland, Germany and Belgium at the same time. De Lommerbergen is the next one I want to try.