Go with unbundled if you can afford to buy the modem once-off. At least if iBurst becomes really bad or some miracle happens and adsl gets good and cheap you're not stuck having to pay WBS for 2 years.
I think you end up paying R200 less for the modem if you enter into a 24 month contract. But the question is whether you are willing to say now you will definitely be satisfied in 2 years time. As said, if you can afford the modem go with that option.