As a USYD college person, my particular college did not have initiations. The entire underlying of ethos of O-week was that there were activities, parties etc. if you wanted to attend them. But not going to rant about USYD colleges here
I think most Melb colleges do not or are benign compared to what you would have heard hyped and worried about on USYD colleges.
I have only ever heard of Trinity having some form of initiation. Just because I remember because the girl on tour at Trinity (who seriously loved the place, was fourth year and like weeping at the thought of leaving and made it seem a little cultish lol) said something cryptic about there always been enough showers except for O-week so I presume they might paint bomb, glitter bomb or feather bomb the freshers or something, but that's just what I inferred, especially as she quickly cut away from it. Though I do recall reading a blog when I was worried about the culture of colleges before going to live in one, that mentioned some initiations at Ormond and surprisingly Newman which surprised given how religious it seems. No tales of forced participation, forced drinking or anything like that though. Just silly dress ups and that type of thing. I'd ask someone at the respective colleges to know, but I've never heard anything bad from friends on that front. Though always remember that O week activities are opt in/opt out, you as an individual always have options of what you want to do with them. I would vouch from what I've hear that St Hilda's, UC, Whitley and St Marys don't have that culture at all, and I'd say those four also don't have the elitism complex of some of the other bigger colleges lol.
Yeah if your grades aren't stellar you'd perhaps have better shot at some of the smaller colleges, but still admission at colleges can be harder than uni itself I feel. St Hilda's is also pretty competitive, as it's the most popular 'chillaxed' college in comparision to the also very popular, Ormond/Queens/Trinity triad. but UC, Whitley, St Mary's etc. tend to not garner as many applications. Oh and don't discount JCH, it's very nice there but not sure if you'd like a very small college. Even at small colleges though, you can always attend tutorials at other colleges through intercollegiate means and that. But, but colleges love volunteer work, sporting prowess and any arts ability seriously, that even if you are not great academically, these can be a serious card in. It's all about being all round. And Tas would give you like location need etc. and perhaps even rural footing depending where in Tas you are from.
UMELB colleges are primarily UMELB students (including VCA)-very small numbers from RMIT and ACU.
Oh and on the tradition thing, I'm sure you will have a great experience no matter which one you choose. All the colleges iirc have the formal dinner at least once a week, so you get to don an acca and get all hogwartsy and be in the intercollegiate mix.