I don't believe there's blatant national flag favouritism anywhere in Europe. There have been many accusations about favouritism in Spain and France, but I consider them to be unfounded. They tend to be based on misperceptions by crews who don't fully understand all the constraints a particular airport's ATC have to work with. Where a minor form of favouritism may exist is with the odd individual here and there. This tends to be based more on personal connections or experiences an individual ATCO may have had with an airline. That's human nature.