I would like to compare OPC UA vs MQTT on basis of the general characteristics of both the protocols such as Overhead (Packets), Security, Information modeling and Reliability. Where can I find some sample data for Overhead, and other characteristics, for each protocol so that I compare them. I need your suggestions. You can suggest any tool to compare these protocols.
I have not seen a OPC UA vs MQTT comparison yet. Bear in mind, that OPC-UA shines most for SCADA systems, MQTT is very good for Publish/Subscribe messaging over unreliable networks like mobile networks.
If low overhead is key for you, MQTT may be a much better fit than OPC-UA. This of course heavily depends on your use case.
You may find this link useful if you're interested in the MQTT overhead: http://stephendnicholas.com/archives/1217
If you're interested in MQTT and security, this blog post series may be helpful to you: http://www.hivemq.com/introducing-the-mqtt-security-fundamentals/
If you're getting started with MQTT, this in-depth blog post series may be valuable for you: http://www.hivemq.com/mqtt-essentials-wrap-up/