I'd like to make sure if my thoughts are correct.
(1) He was the best teacher I have ever had (up to now)
(2) He was the best teacher I ever had (perhaps AmE, the intended meaning is the same as in (1))
(2) He was the best teacher I had ever had (up to a point in the past)
(2) is the one I'm not quite certain about.
I'd be grateful for your comments.
You can also use "He is the best teacher ..." with all those forms if the context is right.