When I need an image to be the focus of the card, I do like medium and large stamps---though I am not sure how to use those really really large cling stamps I've seen at Michaels (it's the one that is a butterfly collage and the stamp is around 7x7!!).
I like to use small and tiny stamps as accents or on envelopes where no coloring is required really.
I do like some cards that some make using a variety of small images together, I just forget to do such a thing.