I really like this visualization of the difference between Deja Vu Sans Mono and Apple Menlo:
(Credit to Jesse Burgheimer)
I decided to take a stab at programmatically generating a similar comparison for all the fonts I’ve been looking at. Here’s the Mathematica code.
It was then easy to generate this for every pair of fonts:
I went through them all and picked out the ones I thought were most interesting:
If you’re interested in seeing the results for every pair, you can download them all.