I know I will get chastised for this comment... but!, I personally find the Librands rear exhaust to be a much fuller, robust sound.
The side pipes do sound excellent but to my ears they do not seem to cover the same range - loosing out of the full symphony that is the rear exits, somehow sounding more mechanical. Also, and perhaps because of their placement, sound less balanced (well you are sitting much closer to one exhaust outlet than the other).
You won't be disappointed with either option but a little like listening to good quality speakers, one person will favour one over another due to the perceived depth and breadth of sound delivery.
