This is interesting. I didnt school here in australia do I get confused on schooling and how it works. My child is 2 so this helps a lot. Thank you for asking this.

Daycare just has longer hours. They still have structure to the learning. Preschool is 9-3.

By Preschool, so you mean Kindy?
I think it would depend on your circumstances. I sent my daughter (my son goes to kindy next year) to a C&K Kindy. School hours 5 days a fortnight. With day care you could choose which days you attend but you would be paying for long day care fees?
My son currently attends a day care and unfortunately then don’t offer a kindy approved program and even though they said they will still teach him, I worry that he will not get the required education that he needs to be ready for prep. This is why I will be sending him to an approved kindy program. I feel that the Kindy is more classroom based where as even though the kindy class at day care is approved they still have that day care feel…lots of play and limited ‘classroom’ style learning.
I guess it comes down to your personal preference and also where your child would be happier.