I've been around here for awhile (so has appianway). This is a perennial question, it pops up every single year without fail.
You can hit the search button and see what we've said on this issue before. The short and skinny of it is repeating year 12 at a school isn't worth it (and to still 90% of peoples opinion, anywhere).
Why not a school? It's a bit embarrassing to go back twice. School environments by their nature focus on other things that aren't related to their subjects, you don't really need that twice. There's a lot less freedom as well. If you find a new school you'll have to make friends all over again.
A TAFE or an adult education centre is a much better option. There's so much less of the needless fluff (or so im told). There is much more freedom and you don't have to endure going back to a school again.
Now, in my opinion, i wouldn't encourage you to repeat at all (unless for some reason you have no other choice). I'll outline why:
1. For most people VCE is hard work or even worse, "hell". Uni is much more relaxed and free. I am doing (or it feels like) less work than in school. It certainly feels far less strenuous. Repeating will unnecessarily put you through the same strain twice.
2. If you repeat the same subjects, it'll be incredibly unstimulating. You might get very bored and it will impact your performance. Choose new subjects and it wont be a walk in the park, you'll be back to square one.
3. VCE subjects to an extent are rather basic, they're not very intellectually fulfilling.
4. You don't need to. There are other options. Depending on your atar, there are various options. One is to go to *any uni* you can get into, take a similar degree to the one you wanted to get into, score highly then transfer into the university of your choice. You will get 'credit' for those subjects, it will count as you having already done them at your new university. So, it's not wasting any time. Furthermore, you get to move on to a more adult life. If you can't get into a uni, there are some tafe diplomas and things that might let you transfer in, i'd contact the university and ask them about your options for getting in. They're a business, they really do want as many students as they can fit.