K&N and KKM are about the same, except the cost. K&N filters are "CARB" certified and will pass any and all emission tests. KKM are not. If you have strict emission tests, they may require a "CARB" certified air filter.
Most places don't look this close at air filters, but some places do. Some people have put a K&N sticker on their intake tube when they have a KKM or some other filter installed and this will usually pass.
Which is best? No one really knows. But either seem to help.
Robb