This is about the 4x5 peel apart Polaroid films. Besides 55, so far, I've been using 52 and 54. 52 yields the nicest prints with a smooth and wide tonal range, but unfortunately it requires coating. It's annoying to have to hand out to your subject a sticky print. 54 doesn't require coating, but is not as nice as 52. What's about 53 ? Is it better than 54 ? Polaroid terms 54 "Proofing" while 53 is "General Purpose".
PS: Polaroid's info is at http://www.polaroid.com/products/instant_cameras/peelapart/4x5/index.html