Microsoft Office because of its rich functionality and the fact that it is pretty much the standard for office suites. Also, Microsoft with Windows 10 are releasing a free office suite built into Windows 10 that includes Word, PowerPoint, Excel, OneNote and I think Outlook. They're universal versions of the apps so nobody has an excuse not to use it really. Google Drive and Docs are far too basic and feature bare for me to give a heck whilst LibreOffice and OpenOffice have remained the same useless junk for years