Hi WhichVoIP,
I had the same question just a while back. I recently moved to JHB and Telkom had been less than helpful in providing me with a land line. Some people on myBB recommended Amobia in some of the threads so I contacted them. A few days later they sent out guys to do a free site survey, they showed up about 2 hours late with no equipment. They simply clambered around to see if I have a line of sight of the tower, which I did but they said they were worried about the power lines and pylons between me and the tower (not sure how a 50-60 Hz isolated connection would really affect a 5.8 GHz microwave...) and told me I'd have to pay for a full installation in order for them to bring a dish and actually test the signal... Not to yammer on about it, as I will be making a post later this week regarding the whole exchange, they were less than helpful and not very customer orientated - seemingly much more interested in getting me to pay an installation fee of R1000 instead of providing me with a service I could at least be sure would work.
A few days later I showed interest on Kawuleza connect's webpage and they phoned me back not even 30 minutes later. They offered to install an antenna a mere 3 business days later (yesterday) and let me test it for free for 5 days. I cannot even compare the difference in service between the two companies. Kawuleza connect came out yesterday with signal testing equipment and did a few tests (I have a nice -59dB signal

) and they will be back this afternoon to do the final installation because there was a small bracket mounting issue yesterday.
How well their service will work compared to other WISPs I am yet to see, but they do claim contention ratios of about 20:1 and provide a service that works out cheaper and potentially better than a fixed land line.
I realise you might be looking for more technical criteria but to be honest I think all of these providers use practically identical tech, I think the type of service they provide might just be a more telling criteria.
I can honestly say I'm really disappointed with Amobia considering how people have been recommending them on this forum.