What is the best paying travel agency?
If there was such an agency, there would be only one agency.
What NedRN has said is fairly correct, but i'll try to shed some light so you can decide what company is going to be the best decision for you.
1) Different companies are going to be using different margins ranging from 20-35%. You should be able to ask your recruiter what margins they work on and if they are unable or refuse to tell you then that should be a red flag. The lower percent margin they take the more money you will make.
2) Different agencies are going to have a variety of contracts and some of these agencies have exclusivity with specific hospitals and areas. If you have a very specific area that you want to travel then you may have to sacrifice pay to get your desired destination. However, if you are open to locations then refer to point one to make the most money.
3) Different agencies are going to have different benefit packages available to you and this often can outweigh how much money you'd make. Some companies will offer 401k, PTO, RSB, Health Insurance, Dental, Vision, etc. Another variable to factor in when looking for the "best" agency.