If the wildebeest migration is a major objective, then there isn’t really a "best" time to visit. River crossings happen between July and October on either the Grumeti or the Mara River, and the calving, one of the most spectacular times to visit, happens in February.  Game action remains excellent through the unfashionable months of March, April and May when the wildebeest start moving off the plains during the rut.  Low visitor numbers make this a great time to visit.

If you’re traveling between December and May, then it’s worth combining Southern Plains with Loliondo, if you’re interested in walking, nightdriving and more of a wilderness experience.

People tend to overlook the green season months in Southern and Western Tanzania, but between December and the end of February can be a great time to visit. Selous becomes humid which makes it less good for long walking safaris but the river is high, everything is green and young animals and migrant bird species are plentiful.

In Ruaha the bush can have closed in a bit making wildlife viewing less easy in some areas, but game remains plentiful, so long as you’re not in a hurry. The water levels will have started rising in Katavi and you may not encounter such large concentrations of animals, but as long as you don't rush things, this is a much more benign season to be there and there is plenty to see.