What is the ERC20 network? ERC20 is the token standard on Ethereum, and the ERC20 network is the everyday shorthand for sending such tokens on Ethereum. USDT ERC20 is the version of the coin issued under it, and many exchanges support it. Its fees are paid in ETH as gas: the gas a transfer uses multiplied by the gas price at that moment, which can climb sharply when Ethereum is crowded. A wallet the owner controls usually needs some ETH to send ERC20 tokens at all, unless a service sponsors the fee or another party pays it.
TRC20 vs BEP20 is mostly a question of chain and fee coin. TRC20 runs on TRON and pays its fees in TRX or through energy and bandwidth; BEP20 runs on BNB Smart Chain and pays them in BNB. Both are usually cheaper than Ethereum. Which is cheaper at a given moment depends on network load, the resources an account holds and the withdrawal charge an exchange adds. TRON addresses begin with T and BEP20 ones with 0x, yet the network should still be picked from the list on both sides.
What is the BEP20 network? Strictly, BEP20 is a token standard on BNB Smart Chain rather than a network of its own, though wallets and cashiers list it as one. USDT BEP20 is the version of USDT issued under that standard, and its fees are paid in BNB, the native coin of the chain, usually at low cost. Addresses on BNB Smart Chain start with 0x exactly as Ethereum addresses do, and one address can exist on both chains. The look of an address therefore never shows which network a payment will travel on.