does it matter which external body i go?
It is more than 15 years since I applied.
And it depends on what kind of qualifications you have ...I think. Some bodies are better for certain qualifications.
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=681&top=29
https://www.canadavisa.com/canada-i...ms/skilled-worker-professional-immigration.4/
You can try this forum to ask questions too.
When my siblings applied they used IQAS because it is Alberta and they wanted to go to Alberta.