I haven't read this whole thread, so this may have come up before.
In MTN's defense I can add the following.
I've been trying both Vodacom and MTN for the last 4-5 months using a Merlin U740 (3G + HSDPA) datacard. Both Vodacom and MTN claim to have full 3G coverage in my area (Centurion CBD). In Vodacom's case HSDPA as well, but in MTN's case I last checked before they introduced HSDPA, so I don't know.
My experience of Vodacom's coverage has been horrible. Even though they claimed from day 1 to have full HSDPA coverage in my area, the coverage is lacking. I often (even now) get only GPRS. In my house, which is two blocks from the lake in the Centurion CBD, I get only GPRS on the ground floor and I get 3G on the first floor about 25% of the times that I try to connect. I have a similar scenario at my office, which is about 2 km down the road. I would love to use Vodacom all the time (because I like their prepaid bundles better), but the lack of coverage/connection instability/network problems causes me to switch to my MTN SIM at least 90% of the time.
On MTN (from the same location), I can't remember ever having a connection problem or having a coverage problem. I'm not sure if I'm getting 3G or HSDPA (I haven't upgraded the cards firmware and it shows a blue LED for both). The connection is fast and reliable in every corner of the house and also at my office.
Of course, I'm only one case, so it's probably not very representative, but it serves to illustrate my point, which is: Vodacom's self-reported coverage is better, that doesn't mean it really is and for me my observed user experience and browsing experience is much more important than what they map on the Vodacom site claims.
Having said that, I was in Bloemfontein this weekend and the Vodacom coverage was excellent. Unfortunately never tested with the MTN SIM to compare.