I would most definitely say that the most boring player to play against would have to be Wraith. Almost every time I play against one they wander around in cloak like an absolute moron.
On the other hand, I would say that the most boring killer to play as would be the Clown. It can be mildly satisfying to slow and stab survivors, but over time it just gets boring after a while.
I'd say either Freddy or Legion, they are both pretty annoying