I think it depends on your capital mostly, for small capital traders it is better to trade altcoins. Just choose those alts that have high volume and those exchanges that do not manipulate volume, for example binance. Of course btc and eth is the best choice to trade, it can make you a huge profit, but you should be able to wait patiently for weeks, months, or even years.
It is simple, if you want to make big profits then go trade altcoins that has smaller market capitalization because they have a bigger room to grow compare to the top cryptocurrencies in the market where their potential market capitalization is almost maximized. Trading bitcoin and other big cryptocurrencies is hard because you need higher skills and it will require more time since the big whales are also playing with you.
OP only looking for a day trade , we know that you can earn much higher profit in altcoin but for day trade i will not concidered this one. the better way to say is to choose wisely what coin will you trade daily.