Since details are all nicely laid down on https://roadtouk.com/preparing-for-the-ielts/ I won’t go into the debate of Ielts vs OET or Ukvi Ielts vs Normal Academic IELTS.
My suggestion would be to take IELTS UKVI on first attempt. And it doesn’t really matter if you take the test from IDP or British Council – there’s no valid proof of one being more flexible than other.
Strive 