Right now, bitcoin is the best option as Bitcoin is very down nearly close to $6,000 and many experts believe that Bitcoin will go beyond $20,000 this year making Bitcoin as one of the best and safe investment options. There are many other coins and options available but investing in Bitcoin guarantee you less risk compared to any other coin and also has a good past record.
6k -> 20k is just 3x, I think there're altcoins that can give more profit. E.g. FSN will release its mainnet and code in 6 weeks and right now only 2x from ico price. Or PAI is a promising blockchain from China 1.1x from ICO price. But agree that Bitcoin is less risky choice.