Pools and maybe Gemini are the only services out there that don't charge any withdraw fees. Gemini is the only exchange I know which has free withdraws. There might be some gambling sites out there also which have free withdraws.
Pools are free for a reason. They are a pool. So what they do is they create a transaction and use a very low fee of like 1 Gwei and include this transaction to every block until someone from the pool finds a block. So what happens is the pool that finds the block is the pool that you are using and doing the free withdraw.
TRC20 is super fast, but the issue is that many exchanges that use tether don't use TRC20 yet. They are mostly under the old OMNI and ERC20 tokens. I don't know why its taking so long for all the exchanges to add USDT on Tron network. Fees are crazy high for ERC20 withdraws. Seems that the omni withdraws would be cheaper.