Can't you just add all of them for the preference of everyone and that's a good option if you're going to be with a stable coin? But if it's with USDT then I would agree with the trc20 protocol because of the fees.
AFAIK, there's also USDT for Bep20.
I think there are still some altcoins that you might be able to use because what you are looking for is very cheap transaction fees, such as TRX, which in my opinion currently still has a good chance.
I think he's going to build a casino that's focusing for with stable coins.