I consider the GVs at both to be very good and impressive but they have differences that may affect your choice:
1. Jambo has 6 GVs and those usually book full during the 11-month window year round. Kidani GVs are often booked full before 7-months out during a number times in the high demand fall season (late Sep to marathon weekend in Jan), but are usually avaialble at 7-months out the rest of the year. Both sets of GV's have four bathrooms, one for each bedroom, and a fourth near the front door and living room.
2. Jambo GV's are all single story on the fifth floor, have a "pool table" room off the living room area, large semi-circle shaped balconies with thatched roofs for each of the bedrooms and living room area, providing ample space for sitting and for outside viewing. (One thing you should do is go to YouTube and see the rooms tours for the GVs -- just search for "Jambo grand villa" or "Kidani grand villa.")
3. KIdani GVs are all two-story on the fourth and fifth floors, with the master bedroom on the 4th floor and the other two on the fifth. Besides the fourth floor main entrance, there is an entry door on the fifth floor. However, if you have guests who cannot do stairs, there would be an issue, because the stairs are the only means of getting from one floor to the other. The balconies are fairly narrow but still useable, and impressive are the windows in the living room that are almost floor to second-story ceiling. At the top of the stairway, there is a somewhat large alcove having a queen-sized bed that pulls out from a couch, a TV, a table and place to sore clothes, and thus provides an extra sleeping area other than just the bedrooms and the pull-out couch in the living room.
4. Jambo has the larger pool and a lot of shaded areas in and near the pool area. The Kidani pool is smaller and has few shaded areas, but it has a much longer slide into the pool and has a large, impressive child (for about 12 and under) water play area. The quick service pool food and drink bars are comparable, but Kidani has a number of tables with chairs under the roof for providing shade that you can use when getting food or drinks.
5. Though both lobbies are impressive, the Jambo lobby is significantly larger, and the Jambo store is quite large, while Kindani's is quite small. (Note, if you are going during Christmas week both have trees and visiting characters in the lobby, but it is the Jambo lobby that has the New Year's Eve event including a live band in the lobby. Jambo, under the lobby on its ground floor, has three restaurants: (a) Mara, a large counter service restaurant with many tables with seats inside and another seating area with tables outside in the shade near the pool area; (b) Jiko, a very good but very expensive table-service restaurant with outstanding food and a huge variety of wines and drinks; (c) Boma, one the best buffet restaurants in WDW. Kidani has only one restaurant, Sanaa, which is a very good table service restaurant (and less expensive than Jiko). Jambo has two bar areas and a lounge area off the lobby that rises up toward the second floor with areas to sit.The only Kidani bar area is in Sanaa.
6. Each has one boarding area for the buses going to the parks and Disney Springs, not overly far from the lobby. Usually, buses going to and coming from the parks stop at Kidani first, although during the morning rush hours each often has its own bus going to MK. A few of the times I have been there, there has, although it is a fairly rare occurrence, been a bus that I got on at a park that, for no apparent reason, stopped at Jambo first before Kidani when returning from the park. There is also a bus that stops and boards near the lobby front doors that runs between the two buildings all day and evening (the distance between the two lobbies is about 1/2 mile, and one can instead walk from one resort to the other without going onto any street). The Disney Springs bus stops at Jambo first going and coming back.
7. If you have a car, parking at Jambo is in a large lot located across the street that runs pass the front of the building. Distance to the lobby is either fairly short or long depending on where you find a place to park. At Kidani, which has two wings, parking is mostly on the first floor under the building in a lot that runs most of the way from one end of the building to the other. There are three elevators along each wing, and you can usually park fairly near the elevator that is closest to your room.
8. Distance from lobby to room is a factor. The u-shaped Jambo building has six GVs three on each side. Two are not overly far from the lobby, the others are far and the last ones are right at the end of the two wings, from which the walk can be quite far. Jambo's walk from the last GV on each wing exceeds the distance from end rooms to lobby at BWV, which many who have stayed at BWV assert are very longs walks. However, both those long walks are nothing in comparison to the potential walk from room to lobby, restaruants, pool, and bus station from rooms at Kidani. The savanna view GVs are spread out over the length of both wings and there are GV's at the end of each wing. The Kidani building, end to end, is about 2/3 mile long, one of the longest single hotel-type buildings in the world (meaning on earth not just WDW). A walk from the end room on the north wing to the lobby takes between 5-6 minutes at a normal adult pace and 7-8 minutes with little kids. The south wing is a little shorter, The longest walk at BWV from end room to lobby usually takes just a little more than 2 minutes and longer with little kids.
9. I consider the two best GVs at Jambo to be the two that are not end units on the Kudo Trail side of the building that have an excellent view of Sunset Savanna. The savanna view GVs at Kidani all overlook Sunset. At Kidani, close to the lobby is a possible request that could avoid the long walk but be aware close to the lobby is the request most often made for rooms at Kidani and thus the one often declined for many because of too many requests, and when they cannot meet a location request, they just put you in any available room in your room category, which means you could end up far from the lobby.. For any savanna view rooms I get at Kidani, I usually put in a request for close to Rafiki elevator or, alternatively, close to the Timon elevator. Either request, if granted, provides rooms with good views and results in your not being very far from the lobby. The Rafiki elevator, on the north wing, provides the shortest possible trip from the building to a pool gate, while the Timon elevator on the south wing provides a fairly quick trip to a door on the second floor that leads directly to the bus station.
