I mostly use the iPad for reading, ebooks, pdfs, saved web articles, HN, etc.

I initially got the biggest iPad but it was certainly too heavy to hold like a book and read comfortably. I switched to an iPad mini which was perfect for reading everything but PDFs, the problem is I read a lot of PDFs. I currently use an 11” and take the cover off to read with it, I find it to be the right trade off between size and weight for me.