Actually, for the popular MTB tours, there are really only two, in Europe, not incl Turkey. This one and Tuscany. Maybe Lakes District. So if you were busy and wanted to do something without doing the actual work to arrange it, it would be one or the other. I'd already done Morocco.
Pyrenees in the most popular MTB tours in US ? Intriguing ! I thought Italy's Lago di Garda was on the top with some other resorts near the Alps. Honestly, the French Pyrenees do not abound of good trips (except going only downhill; I rather belong to the XC type like most of us here). The Spanish side is in my opinion much richer in MB jewels but needs perhaps more advertisement worldwide. Eastern Europe (not only Poland & around where I live) also owns some treasures thanks to a perfect marking and maintained trails (and certainly more affordable from the cost point of view !). If you look for good places to go and need help to find agencies to organize your stay drop me a line. Have you thought about contacting the guy from Isleride who posted the album the other day ? I think Croatia must be amazing.
Yes Brits do often travel in the Pyrenees, that's a traditional touristic destination for two centuries. I think the Isleride guys speak excellent english and probably most of the people who come there are from northern Europe so likely to be english speakers. Otherwise even cheaper: go by yourself somewhere and use the ressources on the web. Just don't be afraid ! :)