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In the current scenario of transition to a Europe-wide circular economy (CE), the Waste-to-Energy (WtE) treatments represent a smart solution to generate renewable energy, reduce landfills and ensure sustainable waste management. The costs and environmental impacts of existing WtE treatments are very different for each available technology. In many cases, their identification is affected by a set of variable boundary conditions strongly dependent on local municipal requirements. In light of these considerations, the paper aims to compare the investment in three different WtE treatments (i.e., incineration, gasification, and flameless oxy-combustion) to identify the best solution to support the current transitional phase towards a CE condition. An overall yearly cost analysis was developed by varying local municipal requirements, including investment, operating, and carbon emissions costs. The overall yearly cost and the revenues, due to energy sales and tipping fees, allowed to evaluate the profitability of the investment in the plant lifetime to identify the best WtE treatment. The investment profitability was evaluated by adopting the Net Present Value (NPV) method by estimating the cash flow statement over the entire plant lifetime. The performance of the three WtE treatments, classified as "conventional" (i.e., gasification and incineration) and "innovative" (i.e., flameless oxy-combustion), were compared in a case study concerning Southern Italy's Metropolitan City of Bari. The applied methodology showed, in this case, that gasification, at the moment, has to be deemed as the most sustainable treatment for MSW management. Moreover, the study proved a high dependence between the carbon price and the profitability of the investment and, thus, in the next future the innovative oxy-combustion technology will gain an advantage over all the other technologies, when carbon price will be higher than 44 €/tonnes CO2. [ABSTRACT FROM AUTHOR]