example: A4, A3, paper boat, book, letter, cardboard, etc.

My vote: receipt (the thing that cashiers give you)

toilet paper

life is trouble without it

Mine is  the old fashioned paper with all those bits in it.

Actually toilet paper is a luxury item...

its quite common here

but i know countries where it is not, so therefor i like we have it here :))

well if the question was related to art

i do waterpainting and therefore i like 400 grams white flat surface paper.

I like the kind were you write on it. I'm not a painter, I don't have that kind of focus.