You should not buy any coin (not important ETH, LTC, XRP etc.) with all your money. If you want to hold only one coin, just only focus on Bitcoin.
If you want to invest in alt coins, diversity is important. Divide your money five to 10 altcoins. For more secure investment focus on top ranked coins with good projects + LTC.
If you are looking for high profit with high risk, you can focus on low ranked coins.