Are both sentences OK?
It was the one of the best shows I ever saw. (yesterday, last year, in the past etc.)
It's the one of the best shows I've ever seen. (just now, today, racently)

Question

Are both sentences OK?
It was the one of the best shows I ever saw. (yesterday, last year, in the past etc.)
It's the one of the best shows I've ever seen.  (just now, today, racently)

Answer

It was one of the best shows I ever saw.
It's one of the best shows I've ever seen.

Note* remove the extra "the" in both sentences.

Answer

I like the first better with "had seen" than "saw", to keep the time sequence consistent.

The second is fine.