I'm afraid we'd need more context - what kind of software would you like to get tested? What do you mean by 'top'? By united states, do you want on-site? USA-based? Company in USA and (some) testers offshore?
Without understanding the problem we're trying to solve I'm afraid I can't be more helpful.
As it was said before, we need more information. What kind of testing do you mean?
Is it for web-based or mobile applications?
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