The design of Tuned Mass Dampers (TMD) is becoming more and more usual in the current design of footbridges. This paper analyzes the optimal TMD design for mitigating pedestrian-induced vibrations in the most frequent loading scenarios, i.e. the single pedestrian modeled as a resonant moving harmonic load and the normal unrestricted pedestrian traffic, modeled probabilistically through an equivalent spectral model. Two optimization criteria are set, concerning the minimization of the structural response and of the TMD displacement. The obtained results are compared with classic criteria given by the literature.