The gnome is by far the most popular PvP mage class in game and arguably the best overall PvE mage. All of the gnome’s racial traits help in PvP, many help in PvE. Not only that, but the small size of the gnome makes it ideal for hiding behind the smallest of objects. Unless you are looking for the gnome, it is very easy to overlook a diminutive gnome standing behind a rock. Out of sight, out of mind is a highly desirable, undocumented PvP talent that is exclusive to the Gnome.
Humans are by far the most lackluster of all the mage classes. Few racial traits help the mage. The spirit attribute presently only contributes to mana regeneration. When compared to the gnome’s racial traits and the formula for calculating mana regeneration based on spirit, the +5 % spirit bonus pales in comparison. I would personally avoid a mage human for game play reasons. Now for aesthetics, the human classes are by far the most “attractive”.