I think bitcoin is the least risky, but also going to pay off the least, at least in short term. You can multiply your bitcoin by trading against altcoins and USD when prices fluctuate and make more bitcoin, too. People speculate bitcoin will be over 25-50k by the end of this year, so that's really good even considering this, 3-6x current prices. You have to consider what other coins are doing too, and weigh your risk against that.