Kai is the better bet. Online gaming isn't all about playing Halo online. With Kai, you pick a game arena boot up your game and you will see all the hosts listed in that arena for your game. It's just simple joining or creating a game from your game. No needing to go to the PC and setting up your host or looking for another room to join.
My view of online gaming is, if your life revolves around playing halo online and you live in the US, XBC is your better bet. If you want to play other games, Kai is your bet.
For some people, XBC is not an option. I live in the asia region and there are almost no players on xbc from over here. So when I join a game, I get kicked 99% of the time (I dont play halo either). To make it worse on XBC, you get hosts saying US only pls. Sure they don't want lag in their games, but it means there are no rooms to play in. Good gaming experience? I think not. It's a different story with Kai. People from the US, europe and asia play together. It's a global community. I started my online gaming on XBC but have gone over to Kai and wont be looking back.
I am looking forward for Unleashx to get Kai implemented into their fine dash and i'm sure many others are too.