Also subjective, but at that size on my machine (13" MBA, non-Retina, El Capitan, Chrome), I find Roboto is a lot easier to read. Interface looks 'greyer' and the contrast isn't so good.
While not the intended use case, I find Interface to be surprisingly readable at extremely tiny font sizes (7, 6, and even 5!).
Sure, you shouldn't be designing an interface with those sizes, but it may be something to consider for some zooming interfaces (primarily maps with lots of tags: street names, POIs, etc.)
Sure, you shouldn't be designing an interface with those sizes, but it may be something to consider for some zooming interfaces (primarily maps with lots of tags: street names, POIs, etc.)