I would still choose to invest in Bitcoin over Bitcoin cash even the it has expensive transaction fee. But when it comes on investing in cryptocurrencies it is always best to diversify, so why not invest in both? It is always the right time to invest in cryptocurrencies if you are going for long term investment, but better to wait for a dip if you want to do short term investment. But since you still don't have any experience investing in crypto, I suggest that focus first in one coin to invest and study how the flow of the market and the best way to start is Bitcoin.