You csn easily split it between both. Since BUSD is the stablecoin of Binance and that's where you intend using the funds, going all in on BUSD wont be a bad idea also. Agreed USDT is the most popular stablecoin but as you said, the interest rate on BUSD is better.
Having both will be the better option considering taking advantage of both side by getting a interests rate advantage on the binance site and USDT being so much popular and has a vast reach will benefit a lot in terms of demand and price. Also, better to have multiple coins rather than being just holding a single coin.