Interface or No?

I've got a bit of a debate on my hands here. I want to either go with a mic preamp and therefore use the built-in apple audio input OR an audio interface.

I've used the first setup (Apple input with preamp) before and it worked pretty well, but will there be a significant quality bump from using the interface?

Any thoughts will be appreciated, thanks!

In short yes. There will be a much higher audio quality when using an audio interface.

You can also consider a USB microphone like this one for example.