What is important to note is that, for fibre and LTE, you need both a network and an ISP.
For fibre, you can’t choose your network (OpenServe, Vumatel, Frogfoot, Octotel, etc) - that is area dependent, and currently we only have one network assigned per neighbourhood/area in South Africa (this may change in future) - but you can choose your ISP (WebAfrica, HomeConnect, RSAweb, Vox etc) (once you know your network).
For LTE however, you could have multiple network operator coverage in one area - but typically not all ISPs are covered by all networks.
So for fibre, one would first check the network covering your neighbourhood, then choose from the ISPs that are available. For LTE you could first decide which ISP you’d like, then check the network if you really wanted to.
In all instances when choosing your final ISP, the criteria most people consider are price and speed. As the costs across ISPs are starting to even out and stabilise (ie price is not such a big pull as most are very closely priced), two of the new factors coming into play is very much customer service and contract legal terms (for example: whether month-to-month, or how easy they make it to switch away).