ADSL IS SHIT.
Ive had optus cable and telstra cable and telstra ADSL(im on now) and iPrimus ADSL.
Telstra cable is the fastest(about 900kbs max), but as said, isnt as constant as optus cable(which is less crowded.
ADSL you get constant speeds, but MAX of about 55kbs. In the city, you get a tad higher, and add that to a 1.5mbs plan, you get around 150-200(190kbs in north sydney)
ADSL is easier, as its just phone line, but its SHIT slow, and more expensive than cable. Cable is a bit of a bitch if you need to get the cable installed from the street(and some people cant get it.full stop) but hell fast and cheaper.
Telstra is a whore, but optus is more of a whore.
The 10gig "unlimited" plan on telstra ADSL is meant to cap you at 10gig to crappy speeds. On optus they do this as soon as you hit 10gig.
Telstra hardly ever does this on ADSL. some proof(i woudnt be able to download 30+ gigs after they capped me to 5kbs speeds):
http://users.bigpond.net.au/asura/owendeddd.jpg
http://users.bigpond.net.au/asura/owned.jpg
Cable they can be a bit omre harsh and cap you.
In conclusion
Telstra ADSL - slow, expensive, but never get capped speeds after 10gig
Telstra Cable - fast,cheaper(but harder to install) can get capped speeds
Optus Cable - fast,cheap, get 12gig instdead of 10, but get capped instantly after the 12gigs.