ERC20 vs BEP20 for cold wallet transfers

Hi my exchange offers the ability to send ETH via the ERC20 or BEP20 network. I have set up both accounts on my cold wallet. Currently sending via BEP20 has a 0.000071 transfer fee, ERC20 has a 0.0035 transfer fee. Is someone able to explain what the difference is in sending via different networks and why this is or isn't a good idea?