I did a massive research assignment for an innovation tech company on this last year.

If by quality you mean 1) able to speak english 2) diversity of code language 3) depth of code language 4) price in terms of salary 5) office cost in terms of real estate and location

Katowice, Poland
Riga, Latvia
Monterrey, Mexico

I have a contact for Katowice who often works with the government to setup offices for major companies. If you're serious and not going to waste my time on theirs, give me a call.