Bitcoin is clearly the king of crypto currencies. I don't understand the battle going on in the community right now, but recently read that Litecoin doesn't have some of the short comings of Bitcoin as far as scaling is concerned. That makes it attractive as an investment.
Similarly, I just read an article about a bunch of big banks using Microsoft's Azure-based Etherium 'Blockchain As A Service' service. With so many big companies behind it, it seems Etherium has a good chance of doing well too (though maybe not the current public blockchain?).
Are there any other reasonable contenders? Dogecoin seems too much like a parody to be taken seriously.
What I'd like to do is put $100 into a few of them and see where it goes (I did that years back with Bitcoin and am very happy).
Apart from the 3 you've mentioned I would suggest you could look at some of the projects that have recently launched ICOs (Initial Coin Offerings). Many of these are plain stupid, and all of them are raising funds for tech that doesn't exist yet, but if that doesn't put you off take a look at the AEternity project (https://www.aeternity.com), and NIMIQ (https://nimiq.com/). They look like two of the better ones to me. Ripple might also be worth investigating.