I took CELPIP in 2015/2016 and didn't like it (not because of my low score). Even while doing it, I didn't really like the structure.
As my CELPIP expired, I had to take another English test - so I opted for IELT. I must say that with the very few sample questions I attempted (especially on listening, I fell in love with IELTS and was blaming myself why I didn't go for IELTS - actually went for CELPIP because I read online that it seems easier.
Long story short,
I enjoyed every bit of my IELTS:
listening 7.5
speaking 7.5
writing 7.5
reading 5.5
More info:
I spent more time preparing for celpip, and if i remember i bought materials.
I didn't have time to prepare for ielts as im currently working - just listened to youtube videos, mostly on speaking and attempted like 10 questions on listening.
also, i got 5.5 in reading because i didn't finish it. i think i only answered 28 out of 40, the rest 12 questions were on those paragraphs question in which you need to read through each paragraph to identify the question (but I must confess the questions are simple and would have been able to get at least 75% of the total 12. Panic set in as I realized time wasn't by my side, so was just not collected again. And of course, I didn't manage my time well - as I knew I spent more time on the simpler question. kind of trying to concentrate on easier questions. Also, reading was the part I least prepared for. I only attempted one past question a day before.
I am not a native speaker.
If you panic speaking to someone, I would say you could consider CELPIP. I prefer talking to someone- and did enjoy my speaking with the examiner who seemed to be super engaged with me - and I tried to show lots of enthusiasm. As opposed to what I read online that examiners carry straight face, i was glad I was lucky to be examined by this examiner.
During my speaking test, at some point I knew I started showing hesitation and repeating few words for clarity - but I don't care.
I feel one advantage of speaking is, if you are the talking talking type and know how to fabricate stories, then shoot for ielts. Looks like examiner sometimes give some prompts based on your questions.
I didnt have time to practice letter writing. I feel there is little control over this as I don;t think my writing can significantly improve within three weeks of registering and sitting the exam.
same goes for reading, but I think reading could be improved by knowing the strategies used in asking and answering questions.
My few cents:
if you have spent lots of years in Canada, you could have a stab at celpip (btw, I feel celpip makes some assumptions that you understand canadian culture, so in my opinion, if you are colonized by the british, like me (lol), go foe ielts.
I just arrived Canada in 2013.
If you can practice ielts everyday for 4-8 weeks, I think you should get 7.5 minimum in all bands (of course that depends on your english level, etc).
I am a spouse of a main applicant, so the pressure to get high score was less.
my spouse attempted ielts twice, first time result (without preparation) was low, second time was last year or so and she got 8 in two bands, 7.5 in one and 6.5 in speaking - said she was panicking, so that affected her speaking score.
one thing i also observed is, if you used the minimum score for both ielts and celipip to simulate your express entry score, you would likely get additional 2 or so with ielts 6.0 minimum.
ielts has lots of materials you can use for preparation. and i can say what you will experience in the exam is 85% similar.
i strongly feel if english is your country's official language (and you not living in Canada/havent lived for up to 6 years or so to understand some stuff about the culture), go for ielts.
after the exam, i was so much in love with it that i felt like registering again, but 300 dollars isnt a joke :-(.
disclaimer - above story was based on my opinions....
perhaps i wasn't lucky to get a celpip exam that was easy - who knows? based on the listening aspect for both exams, it was difficult for me to answer questions on the aspect involving more than two speakers....
also my poor performance in celpip may be because that was first experience writing an English test,
that said, I would go for ielts anytime.
sorry for my disjointed writing and typos.
btw:
celpip score is 8,7,7,6 (I think)- cant remember the bands