IELTS, PTE and OET are all accepted for many purposes, but not for every one. The right test depends on who will read your result, which versions they accept, how you prefer to take a test and which skills are your strongest.
These articles compare the tests and their versions for visas, registration and study, so you can check acceptance first and then choose the format that suits you.
IELTS or PTE for Australia PR? IELTS asks one band in every skill, PTE a different score per skill. Compare both and pick the test that suits your weak skill.