For me, MTN is aimed at business, and for the past 21 years with them, was 99.99% a pleasure. I only had one voicemail issue 8+ years back that took them 5 months to sort, it ended up to be a dual sim issue. Other than that I appreciate the network coverage in SA and roaming outside.
When I had issues, I call 808 and in less than 2 hours every issue would be resolved, then going in to store was always a pleasant experience, so no, I don't have issues with them.
I would say, avoid the franchise stores in the malls, because they serve the masses. They also make you wait days for changes. I understood that they took the franchise stores back, and run it them self, but not so sure, because it always look crap when walking past these stores.
MTN has the portal/website to manage your account, it is better in recent years, but still not 100%, and what a useless app. So my 2c would be, make a good app and website for customers to manage everything account related.
I would like them to respond to emails, (in time), or close the option to mail, because you get nowhere with that (4 month response times on mail)
Edit: O, I would like to try WiFi calling on Apple devices, and not only the one Samsung one..