The destinations are numerous, there are more than 17 national parks and reserves in Tanzania. Some of them must be seen (Ngorongoro, Serengeti, Tarangire), the access of some of them is not easy because they are very far away (Katavi, Ruaha, Selous).
In rainy season, the Selous’s tracks are quite impossible to follow.
But you have a big choice, here are some possibilities :