Best back-lit is tough - I like a lot. I prefer posters with more dark than light, so those areas pop when the poster is backlit. That's why I rotate posters through the lightboxes - I could never make up my mind. I do two new releases each month, so right now I have Lorax and Hunger Games up.
And yes, Porky's Revenge - remember, I'm a big artwork poster fan, and I love the huge Porky's face behind the characters.
I'm looking at replacing my two regular light boxes with the new LED style. Anyone have any experience with these yet?