When selecting avalanche diodes, you must prioritize Breakdown Voltage (VBR), which defines the point at which the diode begins to conduct in reverse bias. Additionally, evaluate the Maximum Peak Pulse Power (PPK) to ensure the device can handle transient surges without failure. For high-frequency applications, Junction Capacitance (Cj) is critical as it affects signal integrity. Always verify the Response Time, which should ideally be in the picosecond range for effective ESD and surge protection.