Definitely a decision to be made based on your preferences.
Jambo, better pool area and the fitness center has massage rooms. Mara is a good quick service restaurant with a full array of food choices, including those with an African flare of flavors. Boma and Jiko are on the ground floor. Both delicious restaurants, although pricey. There's a very nice lounge between the lobby level and the Boma level. We visit everytime we stay here for a late night drink. The store in the lobby is large with many more merchandise options than Kidani. Lobby is bigger and beautiful (as is Kidani's). Savannah views not as good as Kidani's. But some of the standard views (specifically closer to the lobby) have decent pool views, which we've enjoyed in the past. Two bedrooms have 2 bath rooms as previously stated in other posts.
Kidani - Personally I choose Kidani over Jambo every time. I love the extra bathrooms in the one and two bedrooms, absolutely perfect when travelling with my family and grandkids or an all women trip (great spot for a girls retreat!). The rooms are more spacious than at Jambo, and the Savannah views are awesome. (we stay on the Sunset Savannah). Love the restaurant Sanaa! Love the views from Sanaa, and the small lounge there. Love the outdoor firepit/viewing area, where the giraffe and zebra can be so close. During my November trip, staying here, I learned that Sanaa is now offering a quick service breakfast, set up in the lounge area, with use of the tables in the restaurant. They were also taking orders for egg dishes. I hope this continues because I love this option over going over to Mara. Pool area here is very kid oriented, and my least favorite feature of Kidani. I have grandkids, so I like that there's pool area games and music geared for children, but there is zero getting away from the blasting speakers for many hours a day. (If I remember correctly, the games and music start at 11 am and last for hours - so no daytime relaxing at the pool with an all adult party).
It boils down to what your priority is for the resort you stay at. As also previously posted, there is a shuttle that runs continuously between the two resorts. It's also not so bad of a walk.
Just my two cents...enjoy your trip!
Dee