The B55 is the most archetypal-looking break-barrel in existence. It's the break-barrel's break-barrel - if you could only put one break-barrel springer in an illustrated encyclopedia, it or the S70 would be the one to place.
The S54 is, granted, a minger and a moose. And of course the best looking break-barrel is the BSA Mercury-S, but it is not really representative with that swoopy back-block.