Both ETH and BNB have chances for big increase in 2019 as both are doing active development on their own platforms. Personally I vote for ETH as it has to reach some development milestones in 2019.
if they have both, that is a good opportunity because the growth of both is good.
if there are many choices to stay on Ethereum because they may have had it for a long time and they trust Ethereum so they still hold Ethereum.
this year I'm sure Crypto can soar that many coins can be profitable.