I usually look at what is trending and what exchanges I can find rhe specific coins
yes most of people trade usually BTC or Ethereum but it can get boring soon
for example right now many people are trading BTT and tron, since the ICO just finished and there was a lot of hype
do your own research always
For day trading specific coin don't work,only the coin at the trend will give more bumps and dumps where we can generate more profits.BTC and ETH are suitable for fiat to crypto and vice versa for day trading because they want to eliminate risk of losing their capital but trading on exchange means they will trade against BTC or ETH to make profits.