Nuclear all the way! More specifically thorium reactors. In terms of environmental damage per watt generated as well as deaths per watt generated, no other energy source is greener or safer, not even close. Though I also like the idea of every house generating its own household needs of energy from its own solar panels. It's a nice way to build local resilience. I don't think solar can cover the energy needs of industries though.
Fossil fuels: Are scarce (oil, gas) and/or extremely polluting (coal). Also causes climate change.
Wind: Inefficient and unstable. Takes up a lot of space - requires deforestation. Ugly.
Hydroelectric dams: Destroy rivers and fish stocks. Also inefficient (the best rivers for dams are usually already exploited, leaving only marginal rivers to be developed). Ugly.
Geothermal: Only works in a few places (Iceland, for example). Not a solution for most countries.
Biofuel: Limited usefulness. Recycling left-overs is good, but growing crops/trees just to burn them is horribly inefficient.