in my opinion, it depends on needs, buying coins and dividing it not in one coin to be seriously in cryptocurrency trading, you have to think about your portfolio from day one.
No it is not safe to put and depend on one crypto currency because the market will not be stable all the time there will be Profit and loss in the market. So better invest in multiple coins and research the top 5 coins in the market and explore the recent status of these coins, analyse and invest in top coins.
AltCoins like ETH,NEO,Litecoin,Ripple are few trusted coins to invest in...