If you want the least amount of risk with potentially 20% gain, I'd go with bitcoins. or maybe some Ripples
I would choose Bitcoin but not ripple. I choose bitcoin because there is a huge potential that bitcoin will increase in price in the long run. If you want to choose another investment, I'd rather go for a different one, diversifying, maybe gold or other stocks in the stock market. Or if you know someone who is well verse in Forex, you can invest there too.
I am not really a person that is diversifying my investment portfolio since I am only invested in Bitcoin at the moment, but if you are looking for a decent addition to your portfolio, then I would indeed avoid altcoins.
I would go for Gold or choose to add various promising stocks that have their prices still on the lower side since you want the best possible profits.
Altcoins come with a risk level that is way too high for my liking. Yes, you can bank on them, but you can also become a bag hodler.