In my opinion, the best online English courses are the courses by Espresso English. I believe that you will improve your English a lot if you pay for an online course and study hard.
Free courses vs Paid courses
Learning English online can be difficult for some people because they find it difficult to find the motivation and discipline to study consistently. If you have tried many methods to learn English and quit, then you know what I am talking about. Learning English is not something that you can achieve quickly and you need to take time and most importantly, be consistent.
Free options
These types of websites(Duolingo, Busuu) are a great way to get started and they can be fun in the beginning. It is difficult to keep up your motivation with these platforms because they get boring. We learn languages from other people and if we don’t see another person then we get bored.
Paid options
When you pay for something, you value it more. If you spend $100 on an English course then you will do your best to study this course every day. This is what you need to do to reach a high level of English. And that is true of everyone who has a high level of English. There is no magic trick.