I work in a town where the majority of work comes from the government. As a contractor, I generally have to apply for work through agencies which are on the government's preferred vendor's list.

Most jobs are publicly listed and to apply for them, you generally need an agency to represent you by submitting your application with a rate which is usually your rate plus their commission.

I've been trying to figure out what the agencies do, and it seems a large part of what they do is 1) get on that preferred vendor's list and 2) forward resumes.

So right now, my policy is that since their commission affects how expensive I am, one - I don't work with companies that do not disclose their margin. And two, I go for the agency that takes the least amount of commission for the job I want to apply for.

IS that the best approach? I would think applying for a job with the most competitive rate is the best approach but I also wonder whether which agency you're applying through actually matter?

I know some agencies actually build personal relationships with senior managers but how do I know which one? How do I know that actually affect my job prospects?

What criteria should I use to decide which agent I go through for the job?