CTRL-C is not intuitive, especially if you're not english speaking. Apparently Xerox came up with the conventions because of the shapes of the letters, X for crossing out. IBM used to use things like Shift-Insert.
The most intuitive would be the old Sun and HP keyboards, which had keys marked things like "Copy" and "Paste".
X does support so called secondary selection (Windows style), but it is less used than Primary Selection. Again, Primary Selection used to be the standard. X toolkits had primary selection in all text widgets and labels before Windows had any selection in its text widgets. Unfortunately consistency has been broken by people trying to force Windows conventions onto Linux.