Obviously electric trains are best. No air pollution, regenerative breaking, easy to convert to renewables, more energy efficient, and are capable of high speeds (there must be a reason diesel HSR trains don’t exist right?). That being said, literally any train, diesel or electric, hell even coal fired steam trains probably, is better than the car centric hell huge swaths of the world have found themselves in. So for the many lines that are still diesel, or new and proppsed lines that for whatever reason can’t practically be electrified, what are the pros and cons of diesel multiple units vs a diesel locomotive and unpowered carriages? Both are really common, but what are the reasons a train line might choose one over the other, and is one objectively better for most situations, or are they about fifty fifty?