It all depends really. On the one hand, TAFE offers you a chance to do it all again and improve from this year, but you will be a year behind everybody from this year (if that worries you).
Also, if you do your HSC again, and you dont have a lot of discipline, it can end up being a waste of a whole year.
On the other hand, there's transfering through uni. This can be good as it means u dont lose a year, although you have to put up with doing something u may not have an interest in, and for some uni's they have a certain GPA that you must obtain before becoming eligible for a transfer.
So, there are a lot of things you need to be aware of, and it is not an easy decision to make.
But, if you want my personal opinion, me myself, I couldnt go back and do my HSC, even if it were through TAFE. So I would choose to transfer through another course.