I can't speak for the KingKong other than that I have a friend who has one and loved it enough to buy another.
I can speak for the 8bitdo Ultimate Wireless and Pro2.
Although the ultimate wireless is the better wireless controller for latency (2.4ghz) and most features (hall effect sensors, ability to wake the switch) - I still prefer my Pro 2. I find the triggers less fatiguing for long sessions of racing games and the controller is the most comfortable I've ever used. Plus, the convenience of having a switch on the back for 4 (though I've only used 3) Bluetooth compatibility profiles is so convenient, it's the controller I bring with me when going to a friend's because I know that as long as they don't use playstation I can use my controller.
The positioning for the dpad on the Pro2 also makes Tetris much more comfortable.
Both controllers are great though, it would probably come down to whichever one was more comfortable in your hands.
In this same spot.