How to spot Arial v. Helvetica (and Myriad)

Here is a visual guide to the major differences between Helvetica Neue and Arial. And, for comparison, Myriad (Illustrator's default) and Helvetica.

The easiest way to spot Arial is to check the cuts on specific letters. Helvetica's strokes are typically cut either horizontally or vertically, while Arial employs slanted stroke cuts. This is especially visible in the t, r, and C. Helvetica has a tail on the G (Arial doesn't) and a rounded stroke on the R (Arial has a straight stroke).