Hi Deepika and welcome.
I would think most job agencies are quite reliable. There are only a very few that are rogues, like the one mentioned in the previous posts. That was just one bad company that traded under different names when they were found out and wanted to start up again.
Tonix is a good company for medical staff as I have heard about this one, but the others are unknown to me because I haven't needed to use any of them. Perhaps some of the others can say if they have any experience with the other companies you mention. We also have an on-board employment consultancy that we can vouch for and you can find details
here .