For someone who would be taking the GRE in a month, should he practice reading from generic sources like aldaily or The Economist, or focus on passages from the Big Book and other specific sources such as the practice exercises on GregMat’s website?
I would do big book, you have so many passages it’s unlikely you would finish them in a month. Use the short passages for exam practice and use the long passages to practice your reading skills (main idea, simplifying, rephrasing, function etc)