What laptop should I get? HP Pavilion 15-au021tu or Lenovo Ideapad 510 (i5 version)?

Get a MacBook

HP is a USA company, Lenovo is a Chinese company. I don't know what country you are from. But which do you prefer to support?

Go with HP Pavilion 15-au021tu laptop. It's got i5 processor, 8GB RAM & 1TB hard drive
http://support.hp.com/.../c05221092

You didn't specify exact model of Lenovo Ideapad 510 with i5 processor. There's this model with NVIDIA GeForce 940MX graphics card
https://www.amazon.com/...01FJFN2DC/

If such model of Lenovo Ideapad 510 (with i5 processor) is available in Australia, then go with that model, since graphics card is much better than Intel HD (in HP laptop) as it will handle graphics more efficiently
http://www.notebookcheck.net/...033.0.html