the best answer i can give you is: it depends. for short rams, they are all basically the same, the difference in gains is absolutely minimal. for a d series civic, the gain of a ram air is only a hp or two. same with the b series. on the k20 on the other hand, a short ram will give you 10whp by itself. as for cai's, the difference is a bit more pronounced, but your only talking a maximum difference of 2-3 hp between the best and the worst models for b and d series engines. the gain is usually something like 3-6whp max. the k20 has shown to gain over 20whp from a well designed cai. obviously the honda engineers goofed big time on the intake design for the k20, leaving in that much restriction should be illegal. if you took two identical cars, one with a no name cai and one with an aem v2, you wouldnt be able to feel the difference. your talking a difference of 1-2% which is just not detectable in driving. only on a dyno will you see the difference. i rarely say this, but when it comes to intakes, get the cheapie. as long as the filter wont break up or the thing fall apart for no reason, there is little justification for spending the few hundred dollars difference between a high end cai and a no name cai, unless you want to squeeze every last bit of hp from your motor, or your doing a very involved n/a buildup which needs every bit of air you can feed it. a cai is definitely better than a short ram, it sucks up cooler outside air instead of engine compartment air, which is hotter. this is the source of the extra hp, and it also helps prevent detonation by lowering intake temps.