I knew that NetNewsWire had an Attention Report, which would tell you which sites you interact with the most. But just tonight I discovered that NNW can automatically sort your subscription list based on the attention you give each feed. The feeds which get the most activity and attention from you are put at the top of the subscription list.
Go to View → Sort Subscriptions By → Attention.
Patrick Winchell points out that if you keep your subscriptions within a folder hierarchy (I don’t) that NNW will sort the folders based on total attention per folder.