I do not know exactly, but I guess the most appropriate countries in as Japan, Spain, china and Usa, Maybe I can add hong kong and singapur to this list. I thought to meet the needs of the tourists in the regions where tourism is concentrated.
You cant really tell which country trade most in bitcoin, but if I should guess, I will say its likely to be Japan and China. According to a source I read online, Japan was the reason for the price boost around that August 1st, so they are the number one.
Japan use bitcoin for there online transaction but china as of now don't support ICO's which is clearly that they don't support crpytocurrency by there government but for normal people they can trade only which the government don't intervene Asian countries and European countries most likely have the most users of Bitcoin America don't support trading platform investment sites which American is having a hard time involving on those.