If you have your money in banks, you do jot have the complete control. If you save stable coins, most of them are centralized and you do not have complete control and they can fall out of peg and be lesser than the money they are pegged with they become. Example of the pegged coin was Terra Classic USD (UST) which was $1 before but now
$0.01186444If bitcoin price have increased, I can decide to convert some to USD or stable coin. Which one is better? Or is there other alternative which can be comparable with bitcoin in a way it would be independent and having full control characteristic.
It basically depends on what you aim to do with the money that you are saving up. If you are a trader, your best bet is a stablecoin of course, and one that you believe in or that is mostly being used by the market. But, if you are not planning on investing in cryptocurrencies or trading with the money, you should better buy USD and keep them in an account that is safe and that won't just eat up your money or asks you to pay fees or taxes every single time you might make a transaction.
There are a bunch of trusted stablecoins out there, the most used of them being USDT. The one you mentioned, UST, was a very bad experiment by Terra Labs because they didn't peg it with actual USD and wasn't backed by real assets kept as reserve but it was an algorithmic stablecoin that failed and made the whole project fail as well.