The 3 tests are fairly comparable in terms of their level of difficulty. The main difference lies in the way the speaking component is tested. On the IELTS, you speak face-to-face with a human. On the TOEFL and PTE Academic, you speak into a computer. The recording is then evaluated by a human for TOEFL, and a computer program for PTE.
A more important consideration is whether the test is recognised by the university you are applying to. For example since April 2015, many UK universities have stopped accepting PTE and TOEFL test results, and requires all students to complete the UKVI version of IELTS.
theRightU is currently a Gold partner of British Council which administers the IELTS test. We will be most glad to assist students with IELTS registraton at no cost (other than the standard registration fees).