There is no single answer to this question as the strongest 2FA method depends on the specific needs of the user. Some of the more common methods include using a SMS verification code, using a third-party authentication app, or using a physical security key.
The best method for you will depend on your personal preferences and level of security needed. For example, if you want maximum security then a physical security key would be the best option, but if you are looking for something that is quick and easy to use then SMS verification would be a better choice.