Typically, users (sandcarving glass and occasionally stone) will choose a product based on its relevant cost and cutting speed. Aluminum oxide grit is significantly less expensive and has the same relevant recirculation and wear rate as silicon carbide, but is blocky and not as angular, and breaks down in similar shape. Silicon carbide grit is more angular and stays angled as it fractures and stays sharper; the cutting speeds tend to be faster but lighter. It’s not as prone to settle as quickly as aluminum oxide and tends to cling to surfaces.
The use of the two products boils down to the production speeds of an individual facility. If speed and throughput are the most critical, silicon carbide might outweigh the additional expense. The quartz in the silicon carbide makes the media reflective in some light conditions.
Overall, it is a user preference. You cannot tell the difference in surface appearance on glass or stone when either aluminum oxide or silicon carbide; however, on metals, the silicon carbide is brighter and more polished in appearance when paint-fill is not performed. For wood surfaces, aluminum oxide is the better blasting media.