I am a believer in diversification; however, in the crypocurrency word, btc is currently king for longer term and potentially stable investment.... and accordingly BTC is the best game in town... unless you have some insider information about some other alt currency.. Also, the idea of diversification relates to building your financial future in other ways besides crypto-currencies. It can be risky to put all of your assets and time and engergies into crypto-currencies; however, if you end up being correct, there could be a considerable payoff.
ON a personal level, I have less than 10% of my liquid assets invested in BTC... but I have been investing for about 30 years, and I have NOT yet been invested in BTC during a price bubble...