You must buy BTC instead of fork coin like BCH but BCH can be used as a way to diversify your portfolio. none knows when the price of BCH will increase but you should remember that if BCH looks bearish caused by bitcoin.
It's better to divide your money to be used to invest in both the coins. BTC can be used as a safe investment for your money and you can put less to the BCH to get more opportunity to gain more profit from the market.
Think about that wisely dude. You will be facing a very high risk of investing in altcoin.