One of the perennial challenges with 3G broadband is what kind of speed you'll achieve. A study by comparison site Broadband Expert suggests that in the current market, Vodafone is the best performer.
Broadband Expert ranked 1724 mobile broadband speed tests conducted by users in the last six months of 2009. From that data, it concluded that the average speed for users was 1.88Mbps. Vodafone topped the table with 2.2MBps, followed by Optus with 2.1, Telstra with 1.8 and 3 with 1.2.
That data does need to be taken with several grains of salt. The users were self-selecting, so it's impossible to know which locations are being compared, which is essential data in this kind of context. There's no separation of different network types, which means we don't know if every Vodafone user happened to be in an HSDPA area. There's also no factoring in software reliability, which I know from personal experience is a major issue with Vodafone.
On the other hand, data from almost 1,800 people is better in most respects than data from one. For all that, I'd personally be quite surprised if Vodafone could really claim speed superiority over Telstra's Next G network, though in value terms it's definitely a contender.
For a broader view of 3G broadband options, check out our 3G broadband directory.