The English test is one of the few application decisions that is genuinely reversible and expensive to get wrong anyway. Different countries, institutions, and visa authorities accept different tests, and acceptance for admission does not always mean acceptance for the visa.
That distinction matters. Some destinations require a specific secure English language test for immigration purposes even where the university would accept an alternative.
Check before you book
Confirm three things in writing: which tests your target institutions accept, which tests the destination's immigration authority accepts, and the minimum scores including any per-component minimum. A strong overall score with one weak component fails many requirements.
This is why we advise against booking a test before the shortlist exists. Test choice and timing belong inside the roadmap, not before it.
How they differ in practice
IELTS is the most widely accepted and has an academic variant used for university entry. PTE is computer-based with fast results and is widely accepted in several corridors. TOEFL is strongly established in North America. Duolingo is cheaper and taken at home, accepted by a growing but still partial list of institutions, and less often accepted for visa purposes.
Format preference is a legitimate factor once acceptance is confirmed. Some candidates perform better speaking to a person and some to a computer.
Validity and retakes
Scores have a validity period, typically two years. Taking the test too early can mean it expires before a deferred intake, which is a real cost for applicants who move a year.
Build in time for one retake. Planning as though the first attempt must succeed is what produces rushed, expensive decisions later.