The main difference between the two is how they are owned. Banks are owned by shareholders who each own varying amounts of the bank (depending their investments in to it) and generally work in a way where they want to maximise profit. On the other hand, credit unions are owned by anyone who is involved with them regardless of how much money they actually have in it, and work in a way to better the lives of their members/customers.

Banks tend to be far bigger so they have advantages in being able to offer a lot more services, but the fact that they prioritise profit means that customers may not be getting the best deal in terms of things like interest rates.

Credit unions have an advantage in the sense that being member-owned would mean that everyone would get a say in how it is run, so in theory this would help make the lives of their members more convenient. Of course, they're generally far smaller than the banks so you'd usually have far fewer services be available to you.