The lower the better since it is by rank. In the chart I posted, Free Republic is at the top because our rank is lower (better) and growing. Theirs is on the bottom because their rank is much higher (worse), and it had a big dip mid-January.
The worse your rank is, the more prone it is to big zeniths and nadirs since more of your traffic is from fewer people. When they are on more it goes up and when they aren't it goes down.