This chapter delves into the intricate landscape of power amplifiers, shedding light on both existing and innovative criteria essential for their comparison and optimization. Traditional metrics like intermodulation distortion, receiver noise, and transmission losses are complemented by novel considerations such as efficiency and power consumption. The aim is to achieve a holistic optimization of the combined signal-to-noise-plus-intermodulation ratio, factoring in both saturated and nominal power levels, as well as consumed power. Saturated power, constrained by current technological capabilities, serves as a pivotal parameter, particularly in applications like telecommunication satellite payloads, mobile phone handsets, and radio frequency identification systems. Moreover, the design process must navigate the constraints imposed by antenna size, which profoundly influence metrics like equivalent isotropic radiated power and gain-to-temperature ratio. This comprehensive chapter empowers designers to discern between various amplifier technologies and fine-tune the design and operational parameters of each amplifier stage or linearizer. Additionally, the optimization methodology addresses the looming specter of interference, incorporating criteria such as the signal-to-noise-plus-intermodulation-plus-interference ratio, thereby accounting for potential sources of interference from both internal and external systems.