These are the two most widely accepted benchmarks of your English ability. Both give you a certification that is good for 2 years.
a) If you are using the certificate for immigration purposes, take the IELTS General Exam.
b) If you will be studying abroad, then you can choose between IELTS Academic and TOEFL.
c) If you are not computer literate and unfamiliar with a keyboard, take IELTS.
d) If you are more comfortable talking into a recording device than doing the speaking part face to face, take TOEFL.
e) If you are not sure, take a class with me and we can work out which option will be easier for you.