[meeera]

Welcome to the forum!

Firstly: if you want to borrow library ebooks in Australia, a Kindle won't do. So if that's a dealbreaker for you, you can stop right there.

Mobi converts seamlessly to epub with Calibre, and I'd very strongly recommend doing that if you go with a Kobo. It claims "mobi support", but it's patchy and odd issues arise. The conversion is quick and very easy. I buy books from all over, including Amazon, and once I've stripped any DRM (use the Apprentice Alf plugin for Calibre), the conversion comes out just fine.

Ditto in reverse: buy ADE epubs, strip DRM, and they convert into Kindle format if you have a Kindle.

Since collections are a factor for you also, this leans you further toward Kobo. You can manage Kobo collections with Calibre, instead of painstakingly tapping away on the device itself to categorise your books. This also means that if your device is replaced or needs a factory reset, you don't need to do that collections management over again - just restore it as you re-send your books with Calibre.

Now, Kindle has advantages also. If you wish to sync audiobooks with your text reading, for example, the Amazon ecosystem is the way to go. Some people report better customer service from Kindle, and they do seem a bit more likely to throw a discount at you to make you go away; others have good experiences with Kobo (especially more recently, to my mind). Either way I'd recommend buying from a local bricks and mortar store if at all possible, to facilitate a quick and easy exchange in person if you have an issue.

Back on the Kobo side: you can sideload your own fonts, and the inbuilt font and display options offer many more options and fine-tweaking than Kindle does. Some people care very much about this, and some care not a whit.

There are a few more feature and tweakability differences, but that's a starting point.

Whatever you buy, choose a good protective case at the same time. (This is where Kobo falls down pretty badly, IMO - their cases are mediocre and overpriced. Third party ones are readily available from Ebay.)