Not all teas are good for making the zavarka. Since many teas become bitter when steeped too long, it is important to find a tea that will maintain a pleasant flavor even if it remains in the pot for hours. One suggested tea blend for zavarka is Russian Caravan, which is a blend of teas and has a smoky flavor said to be reminiscent of the flavor of tea that made its way across Eurasia by land - the tea leaves naturally absorbed the smoke from campfires and therefore arrived with this particular flavor and fragrance.
However, any Chinese or Indian tea that can be steeped for a long time can be used for zavarka. Herbal or fruit teas can be blended with the black tea to make an even more complexly flavored zavarka.
Learn more about Russian tea culture.