If you are going to book a studio I would recommend Jambo and request Arusha Savanna view along Zebra Trail. Studios at Jambo and Kidani are about the same size. Jambo building offers the larger lobby and larger store, the larger pool (although much smaller slide) which has lots of areas to find shade, and three restaurants, Jiko (table service), Boma (buffet), and Mara (counter service). Jiko and Boma are excellent and the counter service restaurnat is very large and seating is always available (and you can choose to sit outside).
Kidani has a smaller pool but a long slide and the elaborate kids play area, only one restaurant, Sanaa (table service), although it is one of the best restaruants there is on site. It also has ideal parking if you have a car under the building. The busses stop there first going and coming from the parks. I would recommend Kidani if you were getting a 1BR or 2BR because those rooms are much larger than ones at Jambo and have an extra bathroom but with a studio I would definitely stick with Jambo.
Note, any guest at one buidling can use everything at the other but distance door to door between the buildings is 1/2 mile.