I'm one of the 3% to use online shopping, and have tried Coles and Woolies.
I've used home delivery and now use click and collect.
I find the Coles website is easier to use.
Coles also has a dedicated parking area for click and collect customers, you call them on arrival, and within 5 minutes a friendly staff member arrives and packs your groceries in the car.
Woolies require you to find a spot to park, go into the store, wait at the cigarette counter and then they bring your groceries. You're on your own to get your shopping to the car.
The quality of items has generally been very good from both stores. Any time there's a problem with an item, a freecall to a dedicated number gets a credit in your account. This is easier than if I'd physically walked around the store, got home and found an unsatisfactory item - I'd have to go back to the store with the item and my receipt to get a refund.
Online shopping allows me to control my spending, carefully plan for what I need, and take advantage of supermarket specials. Home delivery requires more planning as spots fill fast, however click and collect can be done right up to the night before pick up.
I live in regional NSW, so others may have different experiences depending on their location.
I'd welcome the arrival of Amazon - nothing like a progressive US company to shake things up here.