Waste to energy (WtE) introduces an appropriate solution for municipal solid waste (MSW) disposal and greenhouse gas emission reduction. In this study, for Varamin MSW management, a gas turbine plant with heat recovery unit that is fed by landfill gas (LFG) and combined heat and power (CHP) incineration plant is investigated and compared as two WtE systems to reveal the best plant effectively. Exergy and environmental analyses of two systems are performed. Moreover, the effects of key parameters as decision variables on the energy and exergy efficiencies are identified by sensitive analysis of both systems. Multi-objective optimization of thermal and exergy efficiencies are then done by using Genetic Algorithm (GA) for each studied system. As a result, Furnace in incineration system and Combustion Chamber in landfill system have the most exergy destruction rate. Also, optimization results show that thermal and exergy effectiveness for landfill system are improved by 7.01% and 6.53% respectively; these values for incineration system are calculated to be 45.35% and 92.75% respectively.