There's no question in my mind that, technically, electricity is the best energy source for moving vehicles that start and stop or that travel really fast. The question is whether that electricity is generated on board or comes from elsewhere. The hybrid buses, for example, generate their own electricity on board through a diesel or natural gas engine and store it in batteries and recover it when the vehicle brakes.
The high-speed train requires an electric feed through a wire, just like a subway has a third rail and runs directly off that electricity, which allows it to be pollution free and efficient with very effective increases in speed, acceleration, and deceleration. It's the same for streetcars. It's the same for trolley buses like you have in Vancouver.
But in order to justify the infrastructure investment, which is expensive, you need to have a very intensive service. So there's not much point in electrifying a line where there's a train every half an hour. It makes sense to electrify a line that has very frequent, high-volume service, so that you can spread that investment over a lot of users. If you have a commuter rail line where there's a train every five minutes, the electrification probably makes sense; if you have one that has five trains a day, it probably doesn't.