I vote 9.
I just read and I read quite a lot. The rare times I've needed to use the dictionary, I've had no problems, both Mini and Aura. Sometimes I need to adjust the font size and line spacing, not always. If it's comfortable to read the way it came from Kobo, I leave it alone. I think I've taken a few notes once and was able to look at them when I finished the book, so again, no problems.
Once I had a problem with italics being rendered as bold, half the book must have been in italics. I switched fonts, problem solved. Now, that has been fixed.