Undoubtedly, bitcoin is the first in my list, and I think it goes without saying why. Also, I woul go for IOTA – because of omission of transaction fees and connection with the IoT. Also: Ethereum (as it is the second cryptocurrency after bitcoin by its market capitalization and popularity); Dash (because it provides anonymity and fast transaction with functions of PrivateSend and InstaSend); Stellar (as a blockchain solution for instant international payments with minimal fees); Cardano (because its concept is based on a scientific attitude).