Basically I stick to the 5 star system because that's what goodreads uses, and that's the primary online resource I use for tracking, rating, etc. In my own records I go from 0 to 5, in 1/4 increments (as of now I've only given 3 books zero stars, because usually if I hate a book that much and have no hope of a complete turn around I'll DNF it pretty quickly). I have tried scaled with more precision like 0-100, but I find that there's just too much movement over time, like I would have to re-rate too many books every few years, because now I think a book is 71 rather than 68, or 90 rather than 93.