I have a water fountain outside and every time I turn it on it trips the gfi outlet where it is plugged in. Should I replace the gfi outlet or the breaket?

I would replace the GFI outlet. If it continues to happen... replace the breaker. If that doesn't work... call an electrician.. cause there's a problem. Cheers!

I just commented on this very issue, the breaker gets the blame.

Clue is every time i turn it on it trips the gfi outlet.

Consider the pump motor, that sits in water24/7.Depending on age and quality, and since even commercial and industrial units leak, I suggest having the pump motor inspected first.

Try other devices on the circuit. Have a spare pump?

Do not try the pump in a non-GFI outlet until it passes.