It was Polish WGs when I first started because there were quite a few good ones in Manchester at the time, they usually had good likes lists, decent rates, spoke great English & gave good services but there has been a shortage of them the last few years and those that remain are not the same quality imo.
Now it is English girls by far, specifically WGs from the North West because, generally speaking, there is usually already common ground there from the start, similar sense of humour and banter & such which makes for a relaxed better punt in my experience.