Mobile Ad Hoc Networks (MANETs) represent a dynamic and infrastructure-less network paradigm, where efficient and reliable routing is crucial due to frequent topology changes and resource constraints. This paper presents a comprehensive performance analysis of five widely used MANET routing protocols—AODV, DSR, DSDV, OLSR, and ZRP—under varying network conditions. Using NS-2.35 as the simulation environment, the study evaluates these protocols based on key Quality of Service (QoS) metrics including packet delivery ratio (PDR), end-to-end delay, throughput, routing overhead, packet loss ratio (PLR), and energy consumption. The results demonstrate that AODV and OLSR offer superior performance in terms of delivery and throughput, while DSR is favorable for energy-constrained applications. DSDV and ZRP show moderate performance with limitations under specific scenarios. The analysis underscores the need for protocol selection based on application requirements and highlights the potential of integrating trust-aware and intelligent routing enhancements in future research.