Although both tests seem to focus on the same thing, they do so in different ways, which is why so many students want to know which is better (and even more commonly, which is easier). One of the main differences is the speaking part of the test. For IELTS you are required to take this with an IELTS examiner face to face. For TOEFL the speaking test consists of six questions which you answer into a microphone. These are recorded and sent to an examiner to mark.
The scoring system is also different, with IELTS rating between 0 and 9, with halfway points in between. TOEFL gives a more numerical SAT-type grade, totalling your scores from all the areas. This gives an insight into another key difference. TOEFL is administered by the Educational Testing Service, a non-profit US based organisation, and conducts its test according to US English. IELTS is administered jointly by the British Council, the University of Cambridge ESOL Examinations and IDP Education Australia, and conducts its test in UK English. While the differences are not as great as some assume, accents and spelling variations can cause a problem for some students.