MQTT, AMQP and HTTP are messaging protocols that are commonly used for communicating with resource-constrained IoT devices. HTTP is the standard reference protocol for the REST transportation based on the request/response model, whereas both AMQP and MQTT are message-oriented protocols that use the publish/subscribe model. Message-oriented protocols enhance some of the shortcomings of the complex HTTP protocol by using asynchronous communication, changing the design from a document-centric to a data-centric approach and decreasing the header and message sizes. Although significant technical detail is present on these protocols, their real-time performance is insufficiently elaborated. In this paper, we present an experimental evaluation of these protocols conducted in a homogeneous IoT testbed using a real-time Smart City public data set. We provide the behavioral differences between messaging-based protocols and the REST-based HTTP protocol in terms of message latency and CPU usage for varying traffic loads and message sizes. The results showed that MQTT and AMQP are four times faster than HTTP protocol when comparing the message sent latencies. HTTP uses four times more CPU than the AMQP and MQTT protocols. In summary, message-oriented protocols give more stable and improved results as compared to the REST model-based HTTP protocol for all evaluation scenarios.