Most of the members here will suggest the best based on the returns offered but we should also consider how safe is the investment. If a coin can give you 100x return in an year, it is also very much risky. You see all your invested money disappearing by investing in such a coin. If we judge on those parameters, ethereum seems to be a good investment option. It has go a number of advantages over bitcoins and is the only coin that is supposed to leave behind bitcoins in coming years.