A desktop is more than just panels and widgets. It's also an ecosystem of applications specially written to use its resources and to fit its concepts of usability. That means that when you weigh GNOME against KDE, you need to consider their applications as much as the desktops themselves.
Not all software categories vary with the desktop, of course. The time is long gone when KOffice and the only partly realized GNOMEOffice vyed with each other for users -- although KOffice is becoming increasingly mature, and GNOMEOffice's AbiWord, and Gnumeric are all going concerns, most people just use LibreOffice.
However, in other areas, GNOME and KDE support rival applications whose differences are more than just a "G" or a "K" at the front of the name. In many cases, the applications that support the desktops are a direct reflection of opposing design philosophies.
Here are some of the software categories you may want to consider in choosing desktops. Most of the apps named are installed by default, but some may need to be installed separately, depending on the distribution. Most have alternatives, but, mainly, I am concerned with the apps that most users would regard as standard:
KDE PIM is a collection of individual applications grouped together in a shell known as Kontact. These applications include KMail, and separate applications for contacts, calendars, to-do lists, news feeds, and notes. Similarly Evolution offers email, contacts, calendars, tasks, and memos. Since KDE PIM depends on Akonadi, the KDE personal information manager sub-system and a MySQL database, it tends to be faster than Evolution when retrieving information -- although a failure in this supporting structure quickly renders the essential parts of KDE PIM unusable.
KDE PIM is crammed full of features, some of which (especially in the case of KMail) average users may never use. By contrast, Evolution's features have changed little in the last few years, and can sometimes appear too basic. Not only is the selection of tools more limited in Evolution, but the individual features often offer only basic functionality.
For example, while Evolution's memos are little more than plain text files, KDE PIM offers light formatting, and the arrangement of pages into books. Similarly, while both KDE PIM and Evolution store detailed contact information, KDE PIM includes a tab for organizing email encryption for each contact, a picture, and geo-location data illustrated with a map of the world.
This difference is especially obvious when KMail is compared to Evolution's mail features. While Evolution is easy to setup and more than adequate for everyday email, KMail is more security-conscious and includes graphical interfaces for encrypting email.
At times, though, KDE PIM can be overkill for most users. For many, its color coding only confuses. And while, like Evolution, KMail allows detailed filtering of messages, its default spam settings with Bogofilter are so restrictive that at first every incoming message ends up in the Trash folder until you train it otherwise.
What you think of Gedit depends very much on how it is configured in your distribution. In many distributions, including both Ubuntu and KDE, Gedit is a minimal text editor with only a handful of extras, such as document statistics and a spell check. However, add a plug-in or two, and Gedit quickly becomes more sophisticated, imitating Emacs, Kate, or Vim, and becoming a file manager fit for a system administrator.
Kate also has a Vim mode. However, if you are a coder, you can also set its formatting of such elements as highlighting, indentation and end of the line markers to conform to a variety of programming languages, loading each set of choices into a separate session. Like Gedit, Kate also supports a broad collection of plugins that further extend its capabilities.
Of the two editors, Kate tends to have the better reputation. But the truth is, both Gedit and Kate are what you choose to make of them.
File management is discouraged in both GNOME 3 and Ubuntu's Unity, but for older or experienced users, it remains a basic function of system management.