Google Apps allows for basic text editing when in mobile mode. It offers an option to switch to working with the file using the full desktop-browser tools--but when I tried to work in that mode, Google returned an error message.
Zoho is the only one of the three productivity suites that seems to function normally in iOS using the mobile Safari browser. It also offers the most consistent experience from mobile device to mobile device, and from browser to browser.
Winner: Zoho Organizations willing to capitalize on the close relationship that Office 365 has with Windows Phone 7 and Internet Explorer--or the connection that Google Apps has with Android and Chrome--will probably be satisfied. But Zoho takes the prize overall for mobile platforms and Web browsers.
For individual users, or very small companies consisting of just a handful of users, all three online platforms offer free tools that are roughly equivalent, but with limited features. Businesses that need more-robust productivity tools and capabilities, though, have to pay a price.
Zoho Docs has two pricing options: $3 per user per month, and $5 per user per month. The plans are similar, but for $5 per user per month you can add twice as many workspaces, and you get a few additional features, including the ability to share documents with users outside of Zoho without requiring them to set up a Zoho account. In either case, email is a separate service that costs $2.50 or $3.50 per user per month, depending on the Zoho Docs plan.
Google Apps for Business costs $5 per user per month, or $50 per user per year. Office 365 has a variety of plans for different-size companies with assorted needs; the plan most comparable to those of Google Apps and Zoho Docs costs $6 per user per month.
The $3-per-month Zoho plan seems like the least expensive, but it also omits central features--such as email--found in rival plans. Office 365 offers slightly more features and capabilities than the other two, so the additional dollar per user per month seems justified. However, when you start looking at the more advanced--and more expensive--choices from Microsoft, it becomes harder to make a direct comparison.
Winner: Google Apps Of the three, Google Apps is the best value. The annual pricing of $50 per user per year makes it about a third less per user per year than Office 365, yet it delivers equivalent functionality sufficient for most small and medium-size organizations.
For an extra $15 per month, Office 365 users can also get the license to download the desktop Office 2010 Professional suite. At a total of $21 per user per month, this path is significantly more costly than the Web-only options. It adds functionality lacking in the Office Web Apps, though, and it lets users be productive even in the absence of an Internet connection.