Remember that clearly-ins change from year to year, and so the ATAR for either of those could get lower and you could get in! (not saying it WILL happen, but that doesn't mean you should lose hope either!)
Honestly, if you want to go to Deakin, put it as number 1, then put ACU after it. If you don't get Deakin in your first round, you'll then be considered for ACU. Unless, of course, you don't want to study at ACU - in which case, I wouldn't list it at all. Just list them in order of preference, and you cannot go wrong.
Another point worth making is that you may find the single degree variants of either have lower "clearly-ins", and so it could be a good idea to list them as well and transfer into the double degree after getting some solid marks next year. Of course, don't list them higher than comm/arts just because you don't think you'll get in - nothing will change if you move comm/arts lower other than you DEFINITELY won't get it. If it's number 1 (ie, the first course they'll consider you for), then you still have a fighting chance.