Of course I would say bitcoin, because bitcoin is dominating all of cryptocurrency in the world and the progress of bitcoin is always watch by media, and this is can give good effect for bitcoin to make it more famous and the price will go up easily
For me ethereum, the best reason I choose ethereum for a long-term investment is I believe that ethereum has set itself up to become the largest platform for decentralized services in the world. Ethereum is making progress on its roadmap to support these services for years to come.