I run both :
MTN do not always have the speed, but connection is reliable and stable .
Been playing WoW on both connections where even the slightest instability can cause major mess...Vodacom is horrible, slow ping and constant disconnects.
Vodacom however, IF it's up and running it flies. Unfortunately with that comes a constant disconnect [minimum once an hour if i'm lucky] .
I've managed to keep an MTN connection open for 2 days [had to reboot] , not a chance i will get that with Vodacom.
I get about equal coverage where i am at for both [2-3 bars 3G] .
Service wise: MTN sucks balls, can't view your usage easily online [huge schlep and slow site..inaccurate and slow feedback] . Also no SMS mechanism to get reports/alerts.
Vodacom got a nice site, quick to get to your usage. Also got the SMS functionality.
On the "customer care" side, same crap different provider. If you have to talk to an operator, you are going to wait and will only get "basic" support..anything more complex and you will suffer.
I still however voted MTN, simply because stability and "uptime" is now more important than pricing [it is the same afterall] . The actual speed is a lesser issue, i rather get 300kbps CONSISTANTLY than 800kbps with constant reconnect and slowdown issues .