Make it a character you won't mind seeing four of. I picked a Sylvari because their funky colors and glow are fun.
Racial skill-wise, I'd say that Asura and Humans probably have the best Synergy, but racial skills are typically unimpressive as a whole.
Lore-wise, any race can be a Mesmer. Charr might be less common, as they have a low-key cultural bias against magic, but it's still all good. Humans and Asura may be more common, as they tend to be more strongly Magic-oriented.
If you want to laugh, an Asura. They have well done animations. Lots of personality.
