good post ,
I know the Nationality search in AW is not very accurate but still give us some idea about Nationality & their enjoy list
here is some data and numbers of BB offer in AW and almost 1200 BB offer with no nationality ( but I bet mostly are Romanian )
1529 total
309 Romanian
158 British
33 polish
25 Hungarian
To be honest, based on that statistic British girls are just as bad as Romanina and it is Polish and Hungarians you should go for.
However statistics are just useless in in this case.
There are very high rated Romanina girls in AW which do not offer BB. What you need is brain to figure out where to go and where not to go ... ratings, number of ratings, which other girls got a rating from the same person, area, girl belongs to know group of girls, feedback here etc etc
It is not as simple as nationality.