I'm surprised to not see Quicksilver on a list like this. It's definitely the tool that keeps me coming back to OSX. Most of the "replacements" for it on other platforms (and on OSX) implement very few of its power-user features.
I've quit QS for LaunchBar few years ago (when the author announced the development for QS has ceased) then Spotlight then Alfred. I think Alfred did better than Spotlight as a launcher because of slightly better results (e.g. typing "pho" in my machine list Photo Booth and iPhoto but not the one I want the most: Photoshop) and few little touches here and there where Spotlight didn't get it right (e.g. "press enter to copy" for calculations).
I use file actions a lot (move these files, trash this, etc.), so Spotlight is pretty much out of question.