People say transfers are the best option over graduate, yet there is a lack of information for some unis as to how this works (nuts and bolts) in my experience.
for usyd you apply through UAC to transfer. It generally does not take any extra time if you transfer (I have known many people who transfer). You can apply to transfer from an x/law degree at another university (eg. arts/law) or from just an undergraduate degree (eg. arts).
At usyd, there is no preference given as to whether you are already studying law or if you are already at usyd - everyone wanting to transfer is lumped in the same basket and basically ranked (based on ATAR and GPA) - they take top x number of students for however many places are available. The reason uni's are vague I think about how transferring works is that getting in can depend on how many spots there are (changes every year depending on how many people dropped out), and who else is applying.
Furthermore, getting credit for subjects already studied can change depending on what degree you were doing and at which university - for example, when you transfer you have to apply for credit for previous subjects studied (eg. for arts subjects apply for credit from arts faculty). But this all happens after you get accepted into the degree. They don't generally guarantee what subjects you will get credit for either. But there is room for negotiation.
In regards to transferring over graduate, i'm not sure that one is necessarily better than the other. I have a lot of friends who are doing graduate law at usyd - some in the LLB and some in the JD. Of course there are some differences between JD and LLB now - but not much. Its getting a HECS spot that is really the important thing - you don't want to be paying a huge amount ($20,000 a year or something) to do the JD.