highly recommend And BEyond lodges in Sabi Sands/Timbavati.Been there twice.Also visited Tanzania but unless you follow large herds you have to stick to the roads so visibility can be compromised.South Africa a better bet for wildlife viewing avoid springtime e.g. March the grass is too long.We usually went November

I have been to both countries for the safari experience.If you want to see the mass migration in the serengeti go to Tanzania.we found at the time we were there we had to travel long distances with limited sightings
conversely we visited Timbavati and Sabi sands in south Africa with shorter game drives and plenty of sightings.
I would pick South Africa hands down.I have been there 3 times.It is my ideal winter getaway.I live in BC Canada

I would also recommend And Beyond lodges in south Africa.They are far better than any of the lodges we stayed at in Tanzania and we stayed in some of the best lodges there especially near the Ngorongoro crater and Serengeti.
you will have to do considerably more driving in Tanzania to find the animals
you cannot go wrong with any of the lodges in Sabi sands or Timbavati
If you are not in Tanazania for the migration why go there when the Kruger area has so much more to offer.In the private game reserves you can track the animals off road so much closer sightings.hope this helps