Lol, that's a hard 1. Mokims tulip, or CBG force are the most expensive I think. As for the most used that's a toss up between Barneys and fastbud strains. Hard to say strain but these are the most popular and widely used in the EU as they are Spain, Barcelona and Amsterdam owned. Barneys been the most stable of the 2, but fastbuds are pretty solid too, very few Hermies and so on. Good luck