If I have job in Belgium...

[BlasterBates]

Thanks BB.

Which country would be better for family to live given the choice? Liege, Belgium or Aachen or Germany or Maastricht, Netherlands?

Tax wise you're stuck with the Belgium system, so just a matter of what place you prefer really. Don't really know those places that well. On the whole Belgium is a bit scruffier and less amenities than NL or Germany, but must admit I quite like it. Probably best go for the place with the most expats; and I wouldn't know which one that would be, probably the bigger the place the better it would be.

It does look like that Liege has a nice outdoor pool:



Outdoor pool nearby is a prerequisite when you want to choose somewhere to live. Aachen also has one, probably several.