umm well Kaspa, I'd hardly call myself an expert on the topic of transferring, but i'll tell you what I think anyway.
I hear that internal transfers are generally more simpler (in terms of administrative matters) and easier than an external transfer.
If you dun mind doing a bit of catch up work during ur 2nd year, then enroll at USYD, but if you don't want that extra work then enrol at ACU, where the degree is fairly similar to USYD, so it'll mean less catch up work. But I think u definately need to ask around a bit more and ask the uni students (who are in and about in these forums) for a better opinion....
But yeah did u recieve two offers? Cause the deadline for accepting main round offers is coming up... And USYD enrolments have started...