Simply, there is no right or best country. Every start-up or company is different. The success criteria is unique to every circumstance. Each case has hard and soft criteria that is unique to them. That's why, and not to sound too sale-ay, my company helps companies, probably like you and ISVs and Start-ups outsource software development through our free, proprietary Accelerance Partner Matching System. We've assessed over 1,500 global software service companies, each of which have between 50-800 resources and, “are large enough to scale while small enough to care”. Today we have about 40 Accelerance Certified Expert Software Development Partners in over 20 countries!

Yes, 20 countries and certain locations within those countries chosen with such criteria as globally competitive pricing (e.g., $20-40/hr), under-leveraged yet deep talent pools, highly regarded education systems, political and macroeconomic stability, low employee turnover, strong experience dealing with Western clients (US, Canada, West Europe, Australia...)

Personally, I was a Division Manager at Cognizant since before they were 1,000 people (now they are 180,000!). I Founded, ran and sold a 200 person development shop in Costa Rica. Today, we have successful partners in Argentina, Vietnam, Costa Rica, Ukraine, Nepal, Peru, Belarus, Bolivia, Uruguay, Hungary, India, Mexico, China, Colombia, Romania, Venezuela, Armenia, Philippines, US, and a few others coming on line soon.

This free eBook might help add some insight to your inquiry: http://www.accelerance.com/images/downloads/Rapid%20Referral%20Process%20ebook.pdf

Hope this helps!