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 the opposite, if you have a very small capital it is better to trade the markets that are the most liquid, the markets that have the most volume, and this is because the spread in those markets will be smaller and your chances to make profits will be higher, it is also not true that you need to wait for weeks or months to make profits when you're day trading, that is the whole reason why those that prefer that style of trading engage in it instead of long term trading.
Since Bitcoin is stable enough, what we can do is to hold it for long term and find some other altcoins that we can do for short trading, yes this is fine as we all know it will make you a lot of profit, but before you do that, you should know how to trade well, learn strategies from a lot of experts our there and only start with small capital.