I like both, but they definitely are slightly different.
In addition to the items people called out above here are some to consider.
Pool: In my opinion, the Kidani pool and slide are better/more fun for kids than those at Jambo.
Pool: However, the Jambo pool is much larger.
Rooms: Kidani has dedicated 1 and 2 bedroom rooms while Jambo has lockoffs only.
Rooms: Kidani has more DVC rooms than Jambo, meaning that there is more availability at Kidani for DVC. If you're booking a room in cash, this won't be as much of a concern/consideration.
Rooms: Kidani 1 bedroom rooms have an extra full bathroom (2 bathrooms vs. Jambo's 1)
Rooms: Kidani rooms are larger than Jambo rooms
Rooms: Jambo has Value and Club level rooms if you are lucky enough to book them, Kidani has none.
Layout: Kidani has very long hallways where a walk all the way to the end may be up to 1/3 of a mile.
Layout: Jambo has access to more distinct savannas which may have different varieties of animals staying within them at a given time, and more areas/decks/etc. to look at them.
Layout: Standard-view rooms at Jambo are much more likely to have a savanna/partial savanna view than those at Kidani
Layout: DVC villas at Jambo are all on the 5th floor, so if you want to be down lower/close to the animals, you have a better chance of getting that at Kidani in a DVC villa. The inverse also applies, if you want to be up high, a DVC booking at Jambo will guarantee that for you.
Layout/Rooms: Grand villas at Kidani comprise two floors, which may be a consideration if you have people in your party with mobility issues or prefer a single-floor layout. Jambo grand villas are all one floor.
Parking: Kidani has an underground parking garage, while Jambo parking is in the open/exposed.