There are two versions of USDT, one is
USDT erc20, another is
USDT-Omni.However, if you look at the block browser: etherscan.io, you will find the exact holder addresses of USDT-ERC20 is not too many--only 2787 addresses.
https://etherscan.io/token/0xdac17f958d2ee523a2206206994597c13d831ec7
In contrast, USDT-Omni is more popular and more important for Tether, most of the USDT users are holding USDT-Omni.
Stable coins is very essential for investers to take part in the investment of cryptocurrencies. it's a bridge of the tradiditonal fiat world to the digital currency world. it has many merits, e.g. arbitrage and asset hedge etc. i would not state all the merits; if you are interested in that theroy research, you can find many on the internet.
In terms of USDT wallet. i'd like to recommend you the
bitpie wallet( bitpie.com). It supports over
30 mainnet blockchains, including
BTCBTC, ETH and EOS and so on. Of course, both USDT-Omni and ERC20 are suppported. I have been using it for over 3 years. It is my major wallet storing most of my assets.