Which Recruiting Agenices are Ok?

Hi! Iam a Nurse in India with 15 years work experince, planning to migrate to the US. I still need to undergo the NCLEX and TOEFEL exams. I got some offers from recruiting agencies that assure of preparing me for the NCLEX and TOEFEL in US. But Iam kind of unsure, whether its a good idea to migrate without getting the basic qualifications first. Would it better if I appear for the NCLEX and TOEFEL here in India and then apply or is it ok to join first and appear for the exams there( that is if I stand a better chance of qualifying while preparing in the US).
Moreover, as I have a good stable job as of now, I wish to be sure where I am headed, the offers I have received so far are vague on which state of the US and the kind of hosptial where the job vacancy is?
It would be nice if some one could advice me on some trustworthy recruiting agencies.