On a low carb diet, is whole grain crackers better than eating bread?

It depends. Whichever one has the least amount of carbs is probably best; if you choose bread then choose whole grain bread. Consider whole grain crackers that also have seeds as those will be lower in carbs (such as mary's gone crackers). In following a low carb diet you don't need to completely avoid grains but keep the amount of grains relatively low; whole gluten-free grains are relatively healthy.