I have flown with Kenyan and I rate them very highly. They are certainly better than anything in the West of Africa. CamAir and Ethiopian seem to have gone downhill lately (from a pax point of view), but Kenyan maintain a high standard.
I choose KQ when flying from the UK to Nairobi every time.
Don't know how they compare to airlines from the South of the Continent as I've never been down that way.