This exactly. Personally I use lined paper now, because it makes my writing way more legible, and preparation for the exam.Lined paper makes maths inherently more legible for me.
+1Blank paper (srs). That's what I do anyway- do the maths and then chuck it out lol. Though if you want to keep notes in a central location or look back over your work, then a book would probs be better in which case get lined imo