In my somewhat biased (but only a little) opinion, Vodacom's network peformance as well as Customer Service, is shocking compared to MTN's.
I'll tell you why...
I was an MTN subscriber for good on 4 years, and in those years, I never, ever, experienced a dropped call...one or two not connected calls, but no dropped. I also experienced quite a good level of customer service, most of the time. In general, my MTN experience was largely a good one.
Then...
I was comming to the end of the 2 year contract job, and decided to check out the competition a bit, so I moved to VodaCom, and the wheels fell off.
In the second call I made, after 2/3 minutes, the call dropped, so I called the person back and it happened again, now in the interests of scientific experimentation, I foned 5 other people aswell. All of these calls dropped.
This happens every day, as well as me being guaranteed that 50% of dialed calls will not be successfully connected on the first try, and sometimes not even the 2nd.
Next gripe: Try to activate GPRS with a VodaCom Service Provider...
With MTN, all I had to do was give them a ring, and they activated it. Hell, I think if you dial *123# and follow the instrucations you wont even have to fone them.
Now at VodaCom, you call up their helldesk, and ask nicely for GPRS. They tell you to go away and fone your service provider (Autopage), oki doki.
Give them a call up and they then tell you that they will fax you a form, which you need to fill out and fax back, then they will look at it in 48 hours, then another 48 hours for activation...I don't have GPRS
Those are just some of the more annoying things I have found.
Oh yes, VC is the only network I have ever used that tells you "Number does not exist" when you fone voicemail.
I am biased (only a little) becuase my Father is s founder member of MTN, and is still with the group in Uganda.