Do you only submit to Ezine? Also, how many articles do you have written per niche?
Article Distribution Services thread.
I analyze the keywords which are bringing me the most traffic. The ones where I rank #1, I ignore. The ones were I rank #2-20, I build links for.
That's a rough approximation of what really happens. In reality I'm not quite that rule bound. Sometimes, for example, I just want to rank for a specific keyword despite what the numbers tell me.