Core 2 Duo. I would only use AMD for servers running Linux, and no need for a user interface. To many instruction set incompatibilities between intel and AMD (or at least the potential).
I have been using Intel processors from the very start and they perform very well. Hence, for me Intel Core 2 Duo is much better compared to AMD Athlon X2 Dual Core.
Looking for what you this processor is needed, in most cases Intel Core 2 Duo wins at AMD Athlon X2 Dual Core. Processors of Core 2 Duo of junior models possess very good frequency potential, the best, than at other processors of similar price category. Within the framework of tests we were able to disperse Intel Core 2 Duo more than on 50%, not coming running to multiplying tension and applying only air kuler.
Amd is good in speed ,but it will become heat soon , if it reached maximum temp it will turn off automatically. but in intel this problem wont arise.
I don't know what the best is but I think AMD with their Athlon X2 Dual Core offers better value for money.