Both USDT and USDC can blacklist any address without any reason, So I dont think this is safe way to store 1 Million $ on them.
USDT is big nowdays So what If SEC Sue USDT? in that case maybe USDT lose Value.
DAI, I think DAI is not safe Can lose value 1 day.
Or you can go for fully decentralized cryptocurrencies like Ethereum, although you are not going to like it, because it is not stable, but you can know for sure that the value can increase over the years.