I'm working on a responsive site where the main navigation gets compressed to a "menu" button when at a mobile small-screen size. I feel like there are 2 strong methods for handling the navigation:
Off-canvas -- menu pushes the page content to the right so that only a small portion is showing. Many apps (like Facebook) use this technique, as does Indochino (http://www.indochino.com).
Dropdown -- menu comes down vertically (sometimes pushes page content down, sometimes covers page content). This seems slightly more common than off-canvas -- an example is Nokia (http://www.nokia.com).
I'm struggling to see a major usability difference between the two options, as it seems like it comes down to personal preference. Is there any research specifically comparing the two? Are there particular contexts where one may be stronger than the other?