There are a lot of English exams and certifications around the world. In order to choose the correct one, you have to ask yourself a few questions:
Why do I need to pass an English exam?
Do I need to prove my English proficiency in the area of general English, academic English, business English?
Do I want the results to be valid for a certain period of time (usually 2 years) or for life?
Do I want to study in a country where English is the first language?
How much money can I spend?
Once you know the answers to these questions making a decision should be easy/easier.