I'm a huge Monaco fan. Slightly disappointed that Apple chose a Bitstream Sans derivative for its default monospace font. I don't dislike Bitstream/Deja Vu/Panic Sans/Menlo - it just feels derivative at this point and Apple often take opinionated stances on typefaces.
Nothing beats the lowercase "a" in Monaco.
I feel like it has a bit of whimsy that other fixed with fonts don't have. It's not stuffy or pretentious. None of the bowls are circular or ovular (except for the "o") all of the ASCII range characters are distinct. It looks great in its bitmap or anti-aliased vector versions.
I came to Mac OS recently from Linux and while I like Menlo, I found myself quickly going back to Inconsolata[1], which is really great for long coding hours, and works especially well for me with the dark solarized color scheme.
I've been using Monaco for Powerline for quite a long while now. The main issue is that most of the builtin proportionally-spaced fonts have some glyphs which are difficult to distinguish. Monaco gets the job done but other people prefer slightly different glyph styles or want to make their own fonts, more power to them.
I've been using Monaco 9 since I first started hacking away in HyperCard and BBEdit, and when OS X started screwing up the antialiased version of it I switched to ProFont which looks identical but scales properly
I'm curious why that's the case. Do people generally dislike the system-provided fonts or are the alternatives considered "better"?