My 2c:
Cell C's uncapped packages don't have any FUP from what iv seen and their support is the worst iv ever heard about and used myself out of any ISP. Also they only have one point of presence where they route their traffic through, meaning all traffic gets routed through joburg, so for example if you are in cape town you will get +35-40ms to london (180ms instead of 140ms). For areas that are closer it would be less of an impact on latency obviously.
Mweb's uncapped packages all have an FUP where you get a throttled after using a certain amount, but they have three points of presence: cape town, joburg and durban so latency to international would be better if you stayed outside joburg. Their support is better than cell c, but i wouldn't say its amazing either.
Also i would look into which of these can offer month-to-month where you don't get tied into a contract. Both mweb and cell c aren't really great choices tbh, i would personally go with something else if i had the choice.
