As of the episode Boxed In, Ryan has killed in every season to date.
There is at least one episode each season which doesn't feature a kill from Ryan Hardy.
Ryan came close in killing a main character, namely Joe Carroll in The Final Chapter. However in Resurrection it was revealed that Joe Carroll was still alive to the viewers. Ryan discovered this later in Fly Away, when he saw him briefly in person.
In Forgive, Joe Carroll said that Ryan Hardy had killed more people then Joe himself. However this was not true in season 1 and 2. Ryan however, could have killed more people before the events of the Pilot. This fact hasn't been featured yet in flashbacks or confirmed by Ryan himself.
If Joe's kills prior to season 1 don't count (which is 12 kills), than Joe was right about what he said, since during season 1 and 2, Joe killed 19 people, 6 less than Ryan.