NEO's dividend will actually increase to 15.43% in the beginning of 2018 when the blockrate gets reduced from 27 to 15.even from 1 NEO you will collect GAS if you keep it in your NEON wallet or an exchange like Binance that gives you GAS each month. (Bittrex does currently not distribute GAS)
I don't know if the USDT can be called a coin but I think that it is because it is exchangable in mostly all markets now because of its trend that people are using especially these weeks a lot because it can be used as a backup and covering the loss but holding the money in almost equivalent in dollars.
How? By selling the bitcoins and any other coin when the price is high, converting them to USDT, waiting for the right moment and buy back at the cheapest price possible, thats why the USDT doesn't have a fixed price of 1 USD but it changes +- 0.05 USD.
Most of the alts are not stable and we cant decide which one is stable for daily trading nor for long term as the things change very often and they surprise us a lot.