Hi Amy
The major booksellers in Australia are
Dymocks,
Borders (separate to US Borders) and
Angus & Robertson. The latter two are actually owned by the same private equity company, REDGroup, and are pushing ebooks more than Dymocks. Dymocks did try with ebooks about a decade ago, but only had the iLiad, which retailed for nearly $1000, so it didn't gain much traction.
I tend to favour Kobo, but a lot of people new to the tech will stick with Borders/A&R because they are familiar names and where most will have bought their ereaders (Kobos and Sonys).