If I had $50 to invest now, I would buy 15$ worth of Bitcoins, $10 worth of monero and $10 for ethereum. The rest 15$ I would invest on some of the newer currency or token that have real world use such as storj. There would be more than one currency for the $15 though. I think it is really diversified.
Edit: The investment would have to stay inside some exchange though because otherwise the transaction fee would be more than you end up with!