This article is from the Audio Professional FAQ, by with numerous contributions by Gabe M. Wiener others.
Depends on whom you ask! Over the years, different manufacturers have
adopted varying standards of pin 2 hot and pin 3 hot (and once in a
while, pin *1* hot!). But nowadays most manufacturers have adopted
pin 2 hot. Still, it is worth taking the extra minute or two to check
the manual. The current AES standard is pin 2 hot. [Gabe]