I did take both of the "most popular" English proficiency test. Which one is best it's agreed generally here that it depends on the purpose of you taking the test.
Consider the country that you're going to use the test result for. For USA, TOEFL is more common, for UK, Aus, Eu, IELTS are more widely acceptable.They are both can be compared though. For me IELTS is more real cause the speaking test part you are talking to a person, not a computer. At the end of the day, what matter is whether or not the test result can be accountable and useful for you.