What is the best country to learn English?
There is no simple answer to this question. The two most popular "forms" of English are British and American, so you should decide which you prefer to focus on (unless you prefer to learn Australian or Indian English, etc., for example). Then you need to consider the cost. It can be very expensive to study abroad. Finally, you should consider the cultural aspects and issues of safety in the country you plan to visit. Some students live with a family in the country where they are studying, and this can be a good (or a bad) experience. Being immersed in a foreign culture and making friends with people who live in the country where you study can be very helpful in learning a language.