Depending on your priorities and lifestyle, there are thousands of good answers. But whatever is your preference, consult this very useful map.
It shows different regions in Russia, ranked after the IQ of the locals in the “younger than 30” age bracket (approximately). The way it was done, they took PISA measurements and converted them according to the IQ scale. Where 100 is the general OECD school age average, 98.8 being the Russian one.
As you can see, if you like to rub shoulders with the smartest guys and girls, Moscow would be your top pick with 106.8, followed by St. Petersburg with 104.7, and Tyumen oblast—this is where we pump our gas and oil—with 103.6. On the other side, if you want to dazzle the locals with your superior brain capacity, the best places is North Caucasus, Mary-El on the eastern bank of Volga River north of Tatarstan, and Zabaykalsky krai on the border with Mongolia.