[Blacky]

With the car running and hesitation present, disconnect one at a time. If the hesitation gets worse, that one is OK. If the hesitation stays the same you've found your man. If more than one is bad you could leave the bad one disconnected and continue to pull one at a time and see if there is any change.
After I changed my plugs and one bad coil I broke down and brought it in to a local Subaru specialist. He diagnosed and replaced another bad coil with a spare I supplied.