There are still lots of wildebeest and zebra in the Masai Mara, but most have moved out of the Masai Triangle. They are spread from the central Masai Mara down through the northern Serengeti. There are even good populations north of Seronera in the central Serengeti, but they are likely to turn back as this region is still very dry and there is not enough grazing to sustain them.
The migration will probably start moving south shortly.
The best place to be based at the moment is the northern Serengeti and Loliondo Game Controlled Area. All the camps in this area are reporting good sightings. Some of the best camps are Klein's Camp or the mobile camps that are based in the northern Serengeti. The camps of the Masai Mara are also a good option with lots of game in the Mara. But, the dramatic migration crossings of the Mara River are mostly over.