The short answer is Polyurethane. It is much tougher and cheaper than silicone, but it usually requires a concrete release agent.
The only advantage that silicone has to offer is that no concrete release agent is required. This may be important for certain applications where color pigments and dyes are placed on the mold surface prior to pouring the concrete. Concrete releases can interfere with this coloring process.
Or there may be part designs (e.g., panelized veneer stone systems) that have undercuts in the mold where release simply can not be applied. Silicone is the only sure way to address this.
However, Silicone has been known to cause a white hazing on the concrete – looking similar to efflorescence. The white haze may appear immediately or in the next few days, making it challenging to predict and resolve.