Whatever you use to switch windows. I usually use Alt-Tab, but, e.g. in KDE you can go to a desktop corner and see smaller versions of your windows (updated in real time) and select the one to bring to the front.

I am in the maximize everything camp myself, by the way. There may be applications for which full screen is not needed, but I am not using many of them. A chat window is all I can think of at the moment. Otherwise, my desktop tends to have a console window, with a few tabs open, a browser with a few tabs, and any application I am using, maximized. But applications I may be using are typically Qt creator, Inkscape or Krita.