My go-to is Verdana based on previous empirical tests. It's bigger at the same pt size compared to other fonts, but if you size it down about 1/12th it is just as legible but at a higher characters per inch, which is good for trying to squeeze text into an interface, especially when that interface may be viewed by a group on a projector or screen share.

I just tried to half-ass a similar test by editing the Google Font explorer UI to put them next to each other. Atkinson beats out Verdana for width, by about 4% (eyeballed and envelope math), however it's also 1 pixel taller per line at that size. So it's a more rectangular font. I'd have to think about how I'd want to use it, if I care more about lines per page or characters per column.