How do these different currencies differ?
These different cryptocurrencies differ slightly in terms of ideology, the key difference between them is their monetary supply. More than two-thirds of all available bitcoin have already been mined, with the majority going to early miners. Ethereum raised its launch capital with a presale and only about half of its coins will have been mined by its fifth year of existence.
Ethereum was meant to be used as a way to enforce contracts in a low cost and efficient manner. For example, ethereum can be used to replace the function of Kickstarter, as each individual can pledge their ethereum. This ethereum is held and not given to the project owner until the target is met. Hence, the 10% which is given to Kickstarter is saved and the transaction costs involved in pledging for a new product becomes a lot lower using ethereum vs the traditional method.