Personally I have been with Optus, Telstra and I am now with iiNet.
Optus because Telstra didn't tag the phone line it took 6 weeks to get the phone connected initially, it was fine after that. Telstra was ok, this was an existing service that my ex-housemate had connected. iiNet I am happy so far I have only been connected for about 2 weeks though.
ADSL2 is the most common form of internet connection here. Speed for that will depend on how far away you are from the exchange, and whether your exchange is overloaded, reliability will probably be more of a factor as to how bad your copper line is plus the distance to the exchange. e.g. When I was with Optus I was I think 5-800m from the exchange and I connected at 16Mbps, my parents however are about 3.5km from the exchange and they connect at 2.5Mbps and their connection isn't too reliable, my boss has similar issues. My boss has a backup 3G modem in his modem/router to provide a more reliable connection as his wife needs to stream stuff for work.
I have mostly gone with iiNet as, for various reasons, I was given the option of having no contract or $100 credit plus a modem/router, I chose the credit and modem/router. If I was straight out choosing I would go with Internode as I dislike Peak/Off-peak plans but again, credit and modem/router (which I needed) and quotawise I will not make too much of a difference to me. Internode was bought out by iiNet and are from my opinion effectively the same company, Internode however doesn't have peak/offpeak.
Oh I should also note that I was using a prepaid 3G modem/wireless router for a month before I moved and had my internet connected, I found that it would be quite slow at times, but fine at other times. So I considered it fine for an interim solution until having a wired internet connection. A 4G connection may be better (it is supposed to be faster) but not everywhere has 4G and you may need to check your area if considering it. 3G depending on how much you download/upload is more expensive as well.
I can't comment on cable. If you were in an area with NBN (though getting the initial connection for this can be problematic for new installations, even though mine only took a week but they just needed to swap out boxes rather than install cables) I would recommend at least the 25/5 speeds and you could always up the speed from there if necessary, however unless your in a brand new building this is unavailable in Prahran at this point in time.