Kyurem-Black
Pros
- Base 170 Attack
- Strong physical moves like Fusion Bolt and Outrage
Cons
- Zero good Ice STAB -- Freeze Shock is unreliable unless you use a Z-Crystal
- Must use its lower Special Attack to have a workable moveset
Kyurem-White
Pros
- Base 170 Special Attack
- Much better movepool than KyuB; Ice Beam, Draco Meteor, and Fusion Flare are all options
- Doesn't need to rely on inconsistent Ice STAB
Cons
- Hard walled by Blissey
- Cannot break through Water types like KyuB can
There's a reason KyuW is Ubers and KyuB is OU -- the former is more flexible and proves to be a more potent threat. Unless you know your friend is bringing Blissey and/or bulky Water types, I would recommend using Kyurem-White. Its disadvantages are nowhere near as apparent as Kyurem-Black's are.