Wedding rings come in a variety of materials, each with its own unique set of properties. Scratch resistance is the ability for the hardest materials to resist being scratched or damaged by everyday wear and tear. Crack resistance is the ability of a material to resist breaking or cracking. Examples include dropping or hitting it against a hard object.
Unfortunately, it's not possible to have a ring that is both extremely scratch resistant and crack resistant. The two types of resistances are inversely related. You can have a strong metal ring that's crack resistant like a white gold or platinum wedding band, but the scratch resistance won't be very high. You're more likely to see scratches on this white metal. But you could also have a scratch resistant metal ring like tungsten carbide, where enough pressure against a hard surface can cause the ring to shatter. This is because it's a very hard and brittle metal and can't flex or absorb shock as well as other materials. The good news is that you actually want this for removing your ring during medical emergencies.
Scratch resistance is important if you're looking for a ring that can handle daily wear and tear. But if you want a ring that can withstand dropping, crack resistance is more important. We tend to prefer scratch-resistant over crack resistant rings. Rings are meant to be worn which means you shouldn't really be taking your ring off and accidentally dropping it. In addition, in the event of an emergency, say your finger gets stuck and your ring is in the way, a tungsten ring can be cracked and easily removed.