I use windex. I've tried just about everything. What I have found, is that the towels are very important. I use the Viva paper towels. They are the real soft sort of towel and they are very absorbant.
Once in a blue moon, I will clean the airplane with the Monocote polish. Great stuff. It looks like Armor-all. It even smells like Armor-all. I sort of wonder if maybe it is Armorall. I had a white model that was getting kind of tired and yellow looking. I cleaned it up with the Monocote polish and it came back like new. It brightened up and and got it's shine back. Infact I had that model for 11years before I sold it and it was in great shape. I never had to re-cover it. However, I DO keep my models very clean.