The two mentioned
here are the favourites.
But they can only send along techs who are available. To be honest, the Agencies may not be too bothered about "quality", as they are interested primarily in their "cut".
There are other ways of finding technicians willing to undertake temporary placements.
Like spelling out your requirements right here, for example.
In the event that you find someone who fits the bill, they can always work through an Agent of their choice (for purposes of billing, and payment
etc.).
