I'm using Trust Wallet and I want to buy an Ethereum based token. What is the best option? Buy some Ethereums, then convert it to that token
If you're wanna buying ERC based token and buy it with ethereum will be far better than USDT. The main concern should be on the fees in ethereum blockchain. If you didn't know how to calculate it properly and then you will be wasting your money to pay the fees. When you're using ethereum and your fees will be easily calculated and you didn't need to spend your money to pay the fees two times.
You can buy use ethereum directly instead of using USDT. You need to avoid the fees caused by it will charge you a lot of money just to pay the fees.
buy some Tethers (ERC20), then convert it to that toke.
Which one is better?
Use ethereum instead of USDT to do direct trade to another token. This is the best choice.