Use the completely free word processing/spreadsheet/presentation software that came with my iDevice indefinitely, and I own the software outright.
Two things about that.
iWork is 'completely free' only to the extent that you own an Apple device. Once you switch, you can't use it anymore. The same is true if you only have an iPhone, but not a Mac. iWork for iCloud isn't as powerful yet to be an adequate substitute for a desktop app. In addition, iWork is still terrible when you are working with documents other than iWork documents. Once you have to use Word documents (of which the support in iWork is still disappointing) or ODT files (e.g. OpenOffice files, which are not supported at all but increasingly popular), then iWork is simply a pain. It may very well be that this is not of a concern to you or many other people, but this is, in my opinion, still a very big limitation of iWork.
The other thing is that many people overlook that you don't 'own' the apps you purchase from the App Store, unlike the iWork DVDs that you could purchase before. You are a licensee. For all practical purposes, there isn't much of a difference if you stick with Apple products and your Apple ID for all eternity, but that's pretty much the limit.
An Office subscription solves both problems. Office is the more comprehensive and compatible software and it's more platform agnostic than iWork. Other than what people here think about this licensing model, I think that this is the way forward. As someone who recently made the switch to another smartphone and who uses a Windows and Linux desktop occasionally, the limits of Apple's ecosystem are a huge inconvenience. With that I mean, the fact that Apple products often don't work that easily with other software products and the fact that you cannot just transfer your purchases to another device, is something we should leave behind. This subscription model is what makes that possible. The only negative thing is the price. I used to pay that amount for a Home package, which I used for three years. This is pretty much thrice the price.