For a more conservative approach, you might stick with the best known coins - BTC, ETH, XMR, LTC. A very high risk portfolio might consist solely of well known alts or even include ICOs. Ideally, you might want to mix the two approaches for a better risk-reward. 50% in well known cryptos and the other half in high risk alts. Keep in mind that true diversification is very difficult due to Bitcoins impact on the market.