I use iWorks so I can take advantage of Handoff. If you don't use a Mac, I'd recommend either Office or Google Docs. Google Docs isn't as fully featured but it'll sync up nicely with any other device you have. In fairness Office does this too but for me its either OS X or Xubuntu so I don't get much use out of Office
The Microsoft Office apps for me work the best. Search by Word, Excel and PowerPoint in the App Store. They have SharePoint access, which I use a lot. If you want the most feature-rich office experience then I suggest you use the official Office apps.