Ethereum - because it is a next big think how to use a blockchain in other many ways.
NEO - because I see a big potentional in this coin
Bitcoin - because thanks to Bitoin we have this world of cryptocurrency.
Idap - currently in ICO phase and their idea is really cool to create Crypto derivatives exchange, many positive reviews about IDAP, big partnerships!
My answer will not be something original. I believe that Bitcoin is the best. It is my favorite. As for the other cryptocurrencies, I trust some altcoins and hold them - these are Wings, Kick, Eidoo, Litecoin