Between the two and without going into other choices, I would go for aragonite sand.
-Pros: Massive amounts of surface area to reduce ammonia and nitrite. Unique look. Easy to find and inexpensive
-Cons: Without proper maintenance and tank husbandry, crushed coral can hold in nitrates and be an endless source for nutrients for your tank. The nutrients then have the ability to harm livestock and cause algae, diatom, dinoflagellate, and cyanobacteria blooms.
-Pros: Great amount of area for ammonia and nitrite reduction. With a deep enough substrate, can provide excellent nitrate reduction. Completely natural. When the pH drops to 7.8 or below, the aragonite dissolves rather easy to help replace some Calcium and Carbonate to help balance Calcium and Alkalinity levels that helps the pH. Found in most Fish Stores. Available alternatives such as Southdown.
-Cons: Expensive. Heavy. Improper maintenance coupled with heavy bioloads and overfeeding can cause a build up of nutrients in the sand that can be later released all at once that can cause long term trouble or even a total tank crash.