As far as I know, the 384 and 512 accounts are also supposed to be unshaped. I haven't actually used either one yet, but will prob be downgrading soon

Note tho, with these accounts you must move your line to CS. That said, they are cheaper than Telkom on line rental and Laurie's posted in another thread to say u can keep your line with them (at the lower prices) even if you move away later.
I honestly don't know how much of a speed difference you'll see on the lower line speeds between mweb and CS, considering the lines are so slow anyway. And from what I've been reading, Mweb's still getting decent performance on their uncapped accounts, so they're probably not at capacity yet.
At the end of the day the CS options work out cheaper for me, but with less bandwidth, usually enough for my needs tho, and good speeds pretty much guaranteed. Hence I'm staying with them. Especially since it's still early days for Mweb et al. (although we all know how Afri are suffering).
So to answer your question, my gut says if you want to download a LOT, go for Mweb, they look like they'll be fast for a while yet and don't seem to be applying usage policies so far.
If you want constant performance / speed on a tight budget and with a reasonable "cap", go for Cybersmart.
You'll have to check out their websites for pricing info - I'm downgrading to the CS "R299 for 384k + uncapped weekends + 10GB during the weeks" package next month, probably. REALLY gonna miss my 4Mb line. 25 minutes to pull a 1 hour TV show was NICE.