I have both, and I tend to use them for different missions.
The Burn is sharper, shorter and lighter, making it good for tight, technical runs that have a long walk. It's also more handy in big water because you can bite the edge into the climbing face of a wave.
The Shiva is longer, rounder and heavier. This boat is all about the big drops, punching big holes and getting up to speed in 2-3 strokes. It's not that great in big water or carving runs through tight boulder gardens. It is great in hole fields, though, as the bee stinger will do the watermelon seed effect coming through holes. Landing big boofs (and this thing crushes) is much easier on the back with the rounded hull.