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This article presents both an original contribution and a comprehensive technical review of the existing methods of "energy-ecologic efficiency" and "ecological efficiency". As an original contribution, this work aims at investigating for the first time, through the above-mentioned approaches, power plants fueled by municipal solid waste and hybrids with natural gas. A novel strategy is proposed to solve the main flaws of the existing methods and allow the evaluation of multi-fuel plants in a more practical way. The strategy allows to quantify through a single-score indicator the human health toxicity and climate change potential along with resource depletion due to fuel misuse. It has the advantage of being simple and applicable to any thermal system, allowing quick comparisons between different sources. The major contributions of this work are: (i) to perform a critical analysis, pointing out nuances and limitations of the investigated techniques; (ii) to evaluate systems fueled by urban waste, ranking them among fossil and renewable sources including biomass, biofuel and natural gas; (iii) to study the influence of emission abatement and biogenic carbon offset due to biomass regrowth regarding waste fired plants. As unique findings of this research, are shown the advantages of using urban waste as fuel integrated to gas turbines in combined cycles as an alternative to conventional single-fueled waste-to-energy plants, namely: (i) hybrid plants perform 12-24% better than single-fueled plants; (ii) the only way a single fueled plant can overcome a hybrid plant is if it performs co-generation with a thermal efficiency 27% superior.