I really think it depends on which org you are talking about. Prides HW division is top-notch. From top to bottom they are stacked with fedor reigning supreme.
UFC WW division is the best they have from top to bottom they are also stacked. it is only a matter of time before Hughes loses the belt to any one of maybe 4 challengers to me that makes for a great division. Hence my pick for WW.
I like the Light heavy weights/middleweights (In Pride). To me it seems like that division has the best balance between power and speed, at least right now, after some of the fighters retire I'm sure my opinion will change.