APA is so ugly and unprofessional looking to my eyes. Chicago Manual of Style for life, yo!
As someone with an eclectic enough academic career to have written lengthy research papers in four different disciplines, each utilizing a different style guide, I feel well experienced to pass judgment in ranking, at least these four.
1) ASA
Sociology has adopted its own style guide, which is honestly just APA-lite. As such it's fairly simple but elegant; gets across what's needed and gets out of the way.
2) MLA
Ah, MLA, the style guide for the humanities, disciplines that don't even lay claim to such meager ambitions as "social science". MLA, the style guide for those who undertake research only grudgingly. It's quick, dirty, and to the point. I gotta respect it.
3) APA
APA recently underwent a massive revision that trimmed away a lot of the unnecessary fat. It's still incredibly clunky and behind the times as far as singular "they" goes, but it's not a terrible basis for a style guide.
4) A poke in the eye with a sharp stick
Highly unpleasant, painful even. Still, preferable to the below.
5) Pinkertons
The thing about the Pinkertons is that every historical atrocity that can be associated with them is... more than just historical. It's contemporaneous. You could take every negative assertion that starts "The Pinkertons were..." and replace the word "were" with "are" and remain completely accurate.
6) Chicago
Footnotes? Are you frakking kidding me? In-text citations are right there and you're coming at me with this garbage? Indefensible. Get over yourself, Chicago