CAI vs. K&N vs. SRI

CAI=cold air intake. The it's a longer variation of the SRI=short ram intake. The CAI usually has a filter that sits farther away from the engine so it can pull in cooler air=better engine efficiency=more horsepower.
K&N is a producer along with Injen, and AEM. Take your pick. They are all the same concept and you may only see half a horsepower difference between the three.
Be careful with the CAI, with it being closer to the ground, usually behind the front bumper, you risk hydrolock which can happen if the intake sucks in water. Hope that helps a little. I have an Injen and opted not to intall the CAI extension.

sorry i should have said the K&N drop in air filter. would there be any way to move where it gets the air from like behind the upper grill. some streets around my house have bad flooding problems so that may be out of the question if its sitting low

Just buy the SRI it will do the job.

Unless something has changed recently you are limited to two choices on the 2007+ E's.

A K&N drop in filter or an Injen CAI due to the switch to a MAF on the 2007's.