The quality of the three suites' spreadsheet apps closely mirrors that of their word processors: All three offer clean user interfaces, good compatibility with Microsoft Excel, and only slight -- but important -- variations in their feature sets.
Zoho is the spreadsheet features winner. It will do pivot tables, macros and conditional formatting -- three capabilities that mark the current state of the art for spreadsheets. Google Docs does pivot tables via a plug-in. ThinkFree has promised a new version of its Calc app with pivot tables and macros, but as this was written, it had not yet delivered them.
There is less variation in the user interfaces of the three spreadsheet apps than there is in the word processors, perhaps because they all stick pretty close to Excel. However, there are some differences.
Both Google Docs' and Zoho Sheet's user interfaces are clean and consistent with their word processor's interfaces. ThinkFree Calc's user interface shows the suite's devotion to Office Excel in its menus and feature set.
ThinkFree Calc has a weakness that's also a minor annoyance in its word-processing and presentation apps: Its font rendering is not of the same quality as Google's and Zoho's. Large characters can look a little ragged, and blocks of smaller type lack the smoothness and contrast that the other apps show. It makes the ThinkFree apps look a little retro.
The Google Docs spreadsheet app, like its word processor, offers a limited number of features, but the defaults the designers have chosen are good ones. The charting function is one example: It works differently from Excel, but the difference allows you to select a multicolumn range for the chart -- the first column becomes the labels, and the second furnishes the chart data.
Google Docs gets extra points for its Gadgets, which are plug-ins that let it do fancier things with graphics -- you can create org charts or Gantt charts or interactive charts, for example. Other Gadgets let you use graphic objects in charts, or add Google features like Maps and Search.
Google Docs shows you who else is editing the spreadsheet and offers three tabs that let you publish (show the document on a public page), share (allow others to view and/or edit the document) and discuss (have a live chat with other users -- which raises the question of why we can't have this chat function in Google Docs' word processor, too). Zoho Sheet does something like this as well, although the user interface is different than that in Zoho Write.
All three spreadsheet apps felt slower than their counterpart word processors. Editing formulas or rearranging the columns of a worksheet at times seemed painfully slow. Odd things happened occasionally, as well. For example, rearranging the columns in a relatively simple Google Docs worksheet apparently resulted in some cell references disappearing from formulas. Zoho Sheet repeatedly posted an error message that a "script" in the relatively simple test worksheet wouldn't stop running.
Picking a Winner:
Zoho Sheet clearly has the best feature set -- at least for the moment -- and its integration of chat and publish functions shows why Web-based applications will be so important.