Designing policies to achieve a more sustainable electricity system requires policy-makers to weigh different electricity futures against a wide range of societal, economic, environmental, and technical implications. There is controversy on multiple fronts, as no technology satisfies all the demands of sustainability. Moreover, electricity systems include combinations of interacting technologies, meaning it is not enough to analyze technologies individually. We present a methodology for evaluating the sustainability of a region's electric generation portfolio, using multi-criteria decision analysis. Our framework focuses on long-term capacity planning for resource adequacy and sustainability. We used a regional electricity model and pay close attention to controversies involving offshore wind, natural gas pipelines, and the retirement of nuclear plants. We evaluate a set of generation portfolios under nine illustrative stakeholder preference scenarios across seven sustainability metrics. We find that under many stakeholder preferences, increasing offshore wind from 1.6 to 10 GW and eliminating oil generation scores well. If stakeholders are concerned about the full range of sustainability metrics - including costs, climate change, pollution, land-use, jobs, and safety alongside water conservation and nuclear concerns - then the most sustainable solution is to increase nuclear (to 9.2 GW from 3.5) alongside wind, and back them up with base levels of natural gas and hydro (18.7 and 3.3 GW respectively).