Choosing an agency is really difficult and with the national agencies you can find out more about them from websites so picking through a national one is not hard at all. Personally, I tried after school looking for agencies and eventually gave up and just went with one where the recruiter just kept calling me after I talked with him and always was nice and had a good attitude. All in all if you know that you can get a certain pay with one agency the other usually can match it so just choose one where you will like the contact person that you deal with. I've worked with Medix Health here in Phoenix for a little while and found them to be nice and always able to get me where I want to go when I want it.