There are a few important factors that can help you make your decision.
It is true that IELTS and TOEFL are both tests of English, but it is also true that there are many different forms of English spoken around the world. The IELTS test tends to feature British spellings and idioms, while the TOEFL is more slanted towards American English. For this reason, most U.S. and Canadian universities prefer to see TOEFL scores over IELTS scores.
2. Test Format
The format of the TOEFL test is consistent over time. You can expect that the format you studied will be the format that you see on the test day. On the other hand, the IELTS format often changes.
The IELTS test takes less than 3 hours, while the TOEFL test takes more than 4 hours. TOEFL is longer, which may be more tiring, but also gives you a greater opportunity to succeed.
4. Grammar Standards
The IELTS and TOEFL exams hold test-takers to different standards when it comes to grammar. On the TOEFL test, small grammatical errors are generally overlooked and test-takers’ speaking and writing is evaluated on comprehensibility. On the IELTS test, correct grammar is considered very important.
Overall, the TOEFL is a better test of English proficiency than the IELTS, for people who want to work or study in North America. North American institutions prefer the TOEFL, and its formatting and grading policies make it easier to succeed on. You should only take the IELTS over the TOEFL if you want to live in Britain or Australia.