The Best Cold Air Intake for My 2011 BMW X5 E70

I'm looking for a high-performance cold air intake system to upgrade my 2011 BMW X5 E70. Anyone have experience with AFE, K&N, or Injen systems? What are the benefits and drawbacks of each option? How do they compare in terms of power gains, sound level, and installation difficulty? Help me choose the best one for my vehicle!