CAIs are much, much better. TPR is the most powerful overall and is the only intake that has zero reliability problems. AEM has the second best low end, but the least top end. Injen has the best top end, but actually loses low end (less than stock
). Both AEM and Injen tend to cause bogging (sometimes even CELs), Injen being much more likely. If you're looking for a cheap CAI alternative, pick up one of the eBay ones. They're just about exact replicas of AEM, the only difference being the color and filter, and only cost $50.
If you want the best money can buy, though, get TPR CAI ($180). All of the advantages listed above, plus solid stainless steel construction, adjustable mounting bracket, the best K&N filter out there, and can convert into an SRI if you're afraid of hydrolocking.