Best English courses

Answer 1

If English is not you're native language, the best way to learn is not a course but this (in my oppinion):

First watch films/series/documentaries with English audio and you're own language's subtitles. Later with English audio and English subtitles and lastly without subs at all. Meanwhile, read many English newspapers/articles from editors on a English website ("somesitename".co.uk for example) while using a dictionary. For example: if you understand articles from The Economist well, your English is quite well. Also (try to) write English texts yourself and speak English often (when nobody English is around, just talk to yourself).

When you're quite confident about it, visit an English speaking nation for at least a month and then I think you're able to master this language.

If you are English but you want to improve it, just read/watch what scholars are watching.