The original Delta offers the highest resilience to debris of any of the Tribal range, with extreme tip rake, thickness for both durability and stiffness, and surface area to increase usability at lower speeds (upwind, or in lulls). The Delta Sym was developed for similar conditions, but with slightly less rake- so we could reduce the surface area and decrease drag as a result.
For locations with thick and heavy weed, where getting started is potentially an issue or leading edge drag is substantial, the Delta is the one to go for. If you are confident in starting, and going upwind with slightly less powerful fins, and the weed is not always covering the surface, the Delta Sym has the potential to hit top speeds with less drag. Both designs have been successfully tested in moderate conditions to >45 knots.