Bitcoin is the best coin and the most stable investment available on the market.
Surely we won't know the biggest ATH, but we do know that Bitcoin will grow and breach them all one day.
Point of correction: Bitcoin is not a stablecoin, nor is it a stable investment. The price moves and doesn't stay in one place; it goes up in price and also reduces in price.
A volatile asset can't be a stable one; being stable means the price will remain stagnant in one place no matter what happens, just as they refer to USDT, USD, USDC, and most coins that are pegged with the United States dollar and other local currencies. Even as there is no guarantee that they can't be depegged, they are still good examples of stablecoins, and Bitcoin does not fall into that category.