It is tricky selecting a back row without reference to the rest of the pack as each player brings slightly different strengths.
We need:
guys who won't be easily pushed around
a lineout caller
lineout jumpers
effective work at the breakdown
strong defenders
ball runners with impact
The 7 jersey seems to be between Gill and Hooper, in the absence of Pocock. I suspect that McKenzie will switch between them depending on his tactics, although I think you lose very little with one or the other. You could argue that Gill is a better fetcher and Hooper the more dynamic runner, but they both do all that is required of the position very well. It may be that Hooper starts the first match because McKenzie doesn't want too many first time starters running out, but I'd quite like to see what Gill can do as a starter with Hooper coming late with his strong running.
No 8 is a problem with Hiigginbotham and Palu injured. Mowen looks like the guy for the job, but I hope we make his life easier at scrum time by picking a tight 5 that doesn't get sent backwards all the time. He will do the job well, but my only reservation is whether he can crash through (well, into) an All Black defensive effectively (something like Lelia Masaga would be ideal).
I think the No 6 needs to cover whatever the other two are weak in. So if Hooper starts maybe the 6 needs to be a strong lineout jumper, not so if it is Gill (I think). With Mowen starting at 8, another ball runner would be nice. I think Kimlin could cover both needs very well, and I like the idea of an in form guy from an in form Super team (ie winning) getting a run for the Wallabies.
So that is my long winded way of saying:
Kimlin, Gill, Mowen with Hooper on the bench (even though he has done nothing wrong and I'm happy to see him start).