USA and India for sure. Im seeing Indian spams all around the internet, USA have quality SEO's around the internet.
Culturally speaking India is the worst place to outsource anything to. They just don't function like the western world does, everything can be done tomorrow. There's never any rush to get something completed. Boot strapping at almost everything, if they can cut corners they will do. Do the minimum amount of work possible and deliver the client a shitty product or service. That's what I've experienced and many others have said the same.
hmmmm.. the growth of SEO is rapidly growing. And as i have been an SEO myself, i noticed that it is India which among many country has the most SEO. Next are UK and US. Just my opinion.