Subjectively, I find it easier to impart heavy spin with a flexible frame. Not sure if the "racket science" agrees with that finding though. I find stiff frames to be lacking feel and the ball seems to bounce off them as it would a wall. I like dwell time myself. I also like heavier frames; 13 ounce range. It is all subjective> Sort of like asking what is your favorite color?
If you find a racket that you really like, hoard them.