There is no one energy source that is universally considered the most promising for the future, as different sources have different strengths and limitations, and the most appropriate choice will depend on the specific circumstances and needs of a given situation.
That being said, there are a number of energy sources that are considered to be promising for the future due to their potential for widespread adoption and ability to meet increasing energy demands while also reducing negative environmental impacts. These include:
1- Renewable energy sources such as solar, wind, and hydroelectric power, which have low or zero carbon emissions and are plentiful and widely available.
2- Nuclear power, which has a high energy density and generates low greenhouse gas emissions, but also has significant safety and waste disposal concerns.
3- Advanced biofuels, which can be produced from a variety of feedstocks and have the potential to reduce greenhouse gas emissions compared to traditional fossil fuels.
4- Energy storage technologies such as batteries and pumped hydro storage, which can help to smooth out fluctuations in renewable energy generation and enable wider adoption of renewable energy sources.
It is likely that a mix of different energy sources will be used in the future, with the specific mix varying depending on the region and specific energy needs.