I've used sendle a bit since they integrated with the eBay postage system..
For less valuable items, if there's a big postage price difference or I can't be bothered going to the post office, the pickup option is definitely a bonus.

I've always use Auspost because I've found them to be reliable and really good with lost packages and the compensation.

For same state deliveries, sendle is amazing. Most of my same state orders get to the buyer on the same day.
For interstate packages, they seem to use Fastway and Couriers Please etc. Which has taken around the same time as Auspost, but I'm still worried about lost packages and compensation.

For rural areas, auspost are the cheapest because of the government subsidies I guess.

So far I haven't had issues with sendle, but it's good to have a convenient option now