It's interesting that they all named a serif font as their favourite one. Guess it makes sense when you're typing a lot, and have to re-read it lotsa times...
Personally, I really like the idea of the Futura, that Bauhaus font that only uses basic geometrical shapes like perfect circles, triangles and squares instead of intrinsically curved, uhm, curves:
It's really amazing how he did that, considering that you usually have to twist and manipulate so much in order to arrive at a working, readable font. Like, make the curves of an "O" go higher and lower than the highest and lowest point of an "N", for example, to make them look
the same height. Amazing.
(Oh, and I just found out that the historical plaque left on the moon by Apollo 11 is set in Futura. Way cool.)