If for trading, USDT is mostly used and has more pairs on exchanges that we currently have now. As far as I know BUSD is only used on binance there are few BUSD/alt pair there that you can trade.

But for safety, the popular stablecoins that we have now are backed by a private entity and each of them has their own flaws so what I do is I diversify my stablecoin holdings into BUSD, USDT, and USDC.