Styles and what actually separates them
Hearing aids differ mainly in where the electronics sit and how the ear is coupled to them. Behind-the-ear and receiver-in-canal styles keep the ear more open and suit a wide range of losses. In-the-ear and in-the-canal styles sit in the ear itself and are less visible, but the space available constrains battery life and features.
Dexterity, earwax, how much low-frequency hearing you still have, and whether you wear glasses or a mask all influence which style will work for you. Those are the questions worth asking, rather than which brand has the newest marketing.

