I was pondering using Chicago as default font, but it is pretty 'typecast' (no pun intended, this time ;-)) -- Charcoal (that was used in System 8.x onward) is a lot less 'known' and also, I think, a significant improvement...
But it is actually pretty easy to switch to Chicago in the library -- apart from the clone you mention, there is also a 'plain' TTF version of the original Chicago floating around...