How to express your opinion correctly in IELTS

Which of these phrases would you use in IELTS Writing and Speaking to give your opinion? #shortswithcamilla #ielts #ieltstips

[katherinetreize]

I didn't know that 'I suppose' is informal. Thank you!

[rawcopper]

Suppose has a much lower degree of certainty than believe

[notTheSamePersonAnymore]

"In my opinion" or " I think". Which one is good to use in writing?

[Itsmayy]

I mean. Why is it to be this way?? It seems biased. Speaking and writing is all same it's coming from a person and I don't understand why it has to be put and sort in certain way.