Certainly trading with BTC is the safest option. Trading with alts, especially some bump/dump shitcoins, very easily fills the bag with worthless numbers of some promising projects.
Bitcoin is a safest option for trading in cryptocurrency market, because it has less volatility than altcoins. In trading, either Spot or Margin or Futures, Bitcoin is best for trading too because of its narrower margin of price changes, less volatility than altcoins. Even with Margin or Futures, you will have less risk of liquidations than with altcoins.
With Spot trading, if you open a bad trading position, you can hold your bitcoin like a holder, with acceptance of risk by holding your coins on centralized exchanges, it's not recommended as it is very risky.
Reminder: do not keep your money in online account.