It's in Ubers. Nuff said. Normal Kyurem is in UU, Kyurem-B is in OU.
Kyurem-W and Kyurem-B both hold slightly better bulk, the exact same speed and better overall offensive stats than standard Kyurem. However, Kyurem-B lacks a good physical movepool - it gets a few good moves including Outrage, Fusion Bolt and Iron Head, but such movesets are easily walled by the likes of Heatran. This means Kyurem-B is forced to rely on Special Moves to get by these threats - however Kyurem-W's Special Attack stat absolutely destroys Kyurem-B's, making it more effective overall. Also, Specs Draco Meteor from Kyurem-W is one of the most devestating attacks in Ubers.
But you obviously can't use Kyurem-W if you're making an OU team for more competitive purposes, so you'll be using Kyurem-B in that case.