At Designer Observer, Michael Bierut lists some of the factors that lead us to choose one typeface over another.
On a semi-related note, lately in boring meetings I find myself sketching lowercase g a lot. Usually there’s a little hook at the upper right of the upper ball. I’m still not quite sure what it’s for — maybe to lead the eye in its left-to-right journey across the page — but I love fiddling with its angle in relation to the connector between the upper and lower balls (which is often sort of similar to an open parens or angle bracket). That hook must be some vestigial element, right? If I was less lazy I would look it up.