A mouse, definitely.
Actually, being forced to use a trackpad sometimes (on the train, in meetings, etc.) convinced me to create even more keyboard shortcuts, so now I do 95% of the actions with the keyboard anyway.
The only exceptions are some actions that are not "shortcuttable" (like resizing the sidebars on the IDEs) or actions I don't do often (like clicking the "new email" or the "send" button)
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