I've tried using both Aircrack and Cowpatty to crack WPA with a dictionary attack, and so far my findings suggest that Aircrack is quicker. I find that i get about 36 keys/second from Cowpatty and about 96 keys/second using Aircrack.

Is there any reason to use Cowpatty instead of Aircrack, except for maybe Rainbow Tables, or are there things i'm just not appreciating about Cowpatty?