All of them are a good choice for investment. ETH has been with us for a long time and its trading/market/price history shows that it had potential and it still has. A lot of platforms are based on its blockchain, which is highly usable and flexible, also a lot of tokens (if not almost all) are ERC20 based. Monero on the other hand is supposed to be an anonymous type of cryptocurrency, which is very much needed. About the whole anonymity, I don't know for sure, because I have been reading some articles, that said that his anonymity has been exploited and that it is not different to other cryptocurrencies in this regard - that it is not as anonymous as we think it is. The last one, ripple, I can't really say, because I haven't really looked into the coin yet, but it seems ok.
I would otherwise suggest you to look out for some other coins/tokens too, especially those ones that support some kind of infrastructures (like native blockchain or some protocols).