Hi
CAMANISHPARMARAha - The Economist. You bring up an important point here. While I absolutely recommend reading The Economist,
do not use it as a reference for Sentence Correction. Published in London (with bureaus worldwide), The Economist uses a style of British English that is NOT a perfect match for the GMAT, which insists on American English. There aren't a lot of differences, but the correct use of "which" is one – and that's a meaningful difference on the GMAT.
The New York Times is a better match for GMAT style, although occasionally I'll find phrases there that wouldn't pass as our best answer choice on a GMAT question.
Why does everyone recommend The Economist? It's fantastic training for Reading Comprehension and Critical Reasoning, a great tool for expanding your vocabulary, and perfect for improving your "general culture," as my French friends would say. Indeed, regular reading of The Economist can improve your basic knowledge (and thus comfort level) with a wide variety of subjects AND with graduate-level writing style.