USDT is a questionable "asset" that is pegged to the US dollar. However, pegs inevitably fail. There has been as much as an 11% disparity between the value of USD and USDT which is highly disturbing - a peg is supposed to maintain 1:1 value. If it fails it may cause major issues with Bitfinex due to using USDT as its USD reserves, and lesser troubles for Poloniex which uses USDT but at much lower volume.
Experienced the NuBits peg fail. They recovered enough for an insider escape. A failing peg is a death penalty.
Regarding hodling BTC - always sweet to hear those tunes - seemingly there are some insiders watching ETH these days.