Actually, altcoins are not so highly volatile as Bitcoin. But they are dependent on the BTC price a lot. If it's low, then altcoins will also go down, and vice versa. You can buy any reputable altcoin, just don't invest in some brand new coins. Speaking of a particular crypto, I like the idea of Litecoin being a light version of BTC. LTC is supported by the most crypto exchanges, CEX (https://cex.io/ltc-usd) has finally started trading it, but only with USD at the moment.