Trading is usually done by people in different coins but if one wants to invest in long term plan then he must choose Bitcoin. In terms of trading, other coins in the market always increase quickly due to excess volatility and decrease quickly, so some traders prefer other coins for short-term trading. But if 10 investors were asked which coin is more acceptable in their long-term plans, I think 10 out of 10 would say Bitcoin of course. I myself prefer Bitcoin only for investment but for trading I sometimes try Bitcoin as well as other coins in the market. I can make a lot of profit by trading other coins in the market as well as by trading Bitcoin.
There are large number of coins in crypto world but for the purpose of investment people often choose bitcoin because bitcoin is the only way in which pressure to decide will be minimum. Some people also select ehtereum due to its success but when we see the desires of people so they actually accepted bitcoin more than any altcoin. Some people when making money through trading different coins then they use that amount to buy bitcoin and hold it longer.
For trading you can choose any coin and it will either give you profit or loss but bitcoin is not good for short term trading. People often buy bitcoin and keep it for longer time and at the same time they continue to trade other coins as bitcoin will give them profit after years but altcoins can give you quick earning in little time but the risk is also very high.