The actual gain between different types/brands of CAI are very similar, I will suggest choosing a particular one depends on personal preference such as 1)brand, 2)ease of installation and maintenance, 3)price.
Other than those three factors, I think they all perform very similarly.
Performance wise, I tried K&N drop-in, the engine does pull smoother, not much but noticeable.
Installed the K&N Typhoon last month, it does pull even better than the drop-in and the breathing note sounds much better too.
I believe all the CAIs does the same and the difference between them are not much.
Choose according to your personal preference.
I choose the K&N Typhoon because 1) Well established brand 2) Good feedback from members (However, most of the good brand ie. Stillen, Injen, K&N... got positive feedback) 3) Easy to install and maintenance 4) Price vs Value.
Also, OP, there are TONS of threads in this forum discuss about CAI, from focusing on particular brand to step-by-step DIY guide.
Try to search around the forum, you will get even more info than starting a thread.