Telstra is the single worst option under the sun. Avoid like the plague.
Your two best bets are between TPG and iiNet (which unfortunately isn't on your list), although I've heard some good things about Optus as well. The reason your connection is so stuff is because Dodo is actually tiny (not as small as the other ones there, though) and has little control over the network; they rely on other, bigger providers to handle the majority of their infrastructure which ends up giving the Dodo end users (like yourself) far less performance.
Before you lock into anything, make sure you get quotes on their down and upload speeds. Don't get suckered into high data caps/unlimited stuff, because we all know that's just sales being forgetwits. They use it to try and convince idiots to subscribe to their low quality, low speed connections.
BTW, here's my stats from Telstra in Sydney:
Unless the Australian Government changes the NBN plan to Fiber-to-the-Node, don't expect any much faster than this.
