Basically i do all my comparisons on R400 a month (rental + Telkom 3GB) . That's basically the "entry monthly cost" if you want ADSL .
It is still worth it to get some bandwidth from Telkom ISP, especially at the beginning. I'd say Telkom ISP is most likely the "benchmark" in terms of speed and stability you should get. So i use it particularly to compare and "prove" another ISP is not stable or on par.
If you pay anything remotely close to R400 for wireless/3G (and obviously using at home) , it is seriously worth considering going ADSL.
The advantage of the 3G type offerings is, your "entry monthly cost" can be as low as R20 a month, but the moment you start using 1GB-2GB you're immediately jumping past R400 a month. Unfortunately 3G per/GB pricing is astronomical so it's only economical for relatively low usage (we're talking R200+ p/GB vs. R30 p/GB).
Even Neotel with their R500 for 5GB offering is already past the "break-even" point. So again if you're remotely prepared to pay R500 a month for internet, then ADSL is by far the best option, for stability, bandwidth costs and OPTIONS. It's actually alot of fun being able to pick and choose ISPs and finding a package that fits your profile.
OH and if you now want a 4Mb/s line. Add about R250 per month to all the calculations.
EDIT: Just to add to my last point. If you are considering upgrading your line "at some point" , keep it in mind when picking another ISP. Example, i jumped on one of these "uncapped" offerings but they're all "throttled" at certain speeds, i.e. 384kbps . Now if you upgrade your line, and remain at said ISP you are losing out because now you will still get 384 speeds.
So this is my "real" reason for cancelling my uncapped and moving to ISPs where you pay p/GB (without a speed penalty).