Hi I took both IELTS in 2011 and CELPIP on 2015 for the Express Entry, I am living in Canada as an internationa Student with PGWP and I can tell you pros and cons.
IELTS: PROS.
- Easy to find material to practice (internet, books, videos, tests)
- If you are familiarized with paper exam is better.
- You control your time, the give you 30, 40 or more minutes and you can distribute your time by your own.
- You can erase your answer if you made a mistake and you have enough time
- Its valid not only in Canada, but also in USA, UK, Australia, New Zealand, etc.
IELTS. CONS.
- If you learn american english or you live in Canada is difficult the accent sometimes, IELTS uses british accent, differente kinds of accents and even australian accent. (for me is the worst).
- You will be watched for 3 teachers during the test, and walking around through the applicants
- The test takes at least 3 hours.
- Sometime you take the reading, writing and listening one day and you have to go back for the speaking test.
- The speaking test is with a real person ( a british teacher usually) alone in a small room with camcorders and audio recorders ( a little bit stressful).
- The results takes a long time to be delivered around 1 month.
CELPIP PROS.
- You manage your time, so you can do it in less than 3 hours.
- The exam is entirily in a computer (for me is easy and relaxed)
- No more than 2 teacher watching you and in a long distance .
- The accent is neutral (no british or australian accents)
- The software is easy
- The questions are shorter than IELTS questions
- A little bit cheaper than IELTS ( at least here in Canada)
- The result are deliverede soon in two weeks or less since you take the exam.
CELPIP CONS
- A few free material to practice
- Sometimes during the test the time is not enough to answer and that can give you an extra stress (30 seconds or less for answer and the the sysytem ready or not will pass to the next question).
- The reading and writing sections are no son long as IELTS.
- The speaking section are short answers buy many of them, and a few time to prepare.
- Its only valid in Canada.
In my personal opinion if you are living in Canada go for the CELPIP, for me was less stressful than IELTS, however i feel more confortable on listening with the IELTS.