There is no difference in term of line that shows the graph of two currencies however there is difference between the percentage of dip and recovery in the price.
Image Source : https://coinmarketcap.com/currencies/bitcoin/#charts
both have weekly low before 19th March and recovery of both coins started at around at the start of 19th march.
Image Source : https://coinmarketcap.com/currencies/ethereum/#charts
some people consider that Ethereum can replace Bitcoin or Bitcoin cash can replace Bitcoin this year but until know this doesn't seems to be the case. Any currency which is going to replace Bitcoin will replace it when there will be some kind of upward trend in the price of bitcoin.