Better way first: narrow down your selection to where you would like to go.
Research the hospitals in the area. You should try to be selective of the hospital first, not the agency. Find a hospital that you like, then find out if they use any travel companies. And if so, which one or ones? You will have a much better time this way and not get placed at someplace that you want to run from.
Remember that most recruiters just need to fill a spot so that they get their commission. They don't always take your best interests at heart. And no matter which agency that you go with, it is all going to come down to the person that you work with.............it can be a great company and you immediately sign with them, only to get the person from hell to handle your account.