In terms of OPS+, Killebrew's 1967 (173) was nearly the equal of his 1969 (177). He had "only" a .269/.408/.558 (.965) in 1967 compared to .269/.427/.584 (1.011) in 1969, but 1967 was a tougher environment to hit in. In 1969, he had the advantage of expansion and a lower mound.
But I still lean Carew.