Again, from Reddit, someone pointing that Asuras had an advantage on WvW due their size, like gnomes in World of Warcraft.
There are two points on this: A technical point and a psychological point.
First, the technical (’cause it’s the easiest one): What we are talking here is called “hit-box”. That’s the box around your character that, when a projectile/swing crosses it, the game identifies as a hit — and also the opposite: if it goes outside this box, it’s a miss. Game developers do this to reduce the calculations, so they don’t need to check all the corners and different pieces that make your character: It hits the box around the character, then they will take damage. Pure and simple.
In this aspect, ArenaNet said that all races hit-boxes are standardized. This means that a Charr will have the same hit-box as an Asura. This means that, when playing with your Charr, you may notice that some projectiles will cross your character and you’ll take no damage; on the other hand, when playing with your Asura, a projectile may pass close to you, you may see it not hitting you but you’ll still get damage (surely, I’m assuming that Charr model is a bit larger than the default hit-box and the Asura model is smaller than the hit-box).
So, in the technical side, you don’t need to worry about sizes when creating a character: Picking one doesn’t mean you’ll be harder or easier to be hit.
Then we have the psychological point, using the gnome example: Gnomes and Asuras are smaller than the other races and people may not see them as a threat — or even ignore them due their size. As an ex-WoW player, I must say that gnomes were my first target, because I thought they would keep doing that annoying noises all the time, so I didn’t agree with the guy original point, but one can see where he was going.
In this point, I’d agree with him, if it wasn’t for the Asura habit of jump, somersaulting and doing all those flourish movements. Those get attention and make the Asura visible to other characters. Thus, if you think it would be easier to go unnoticed as an Asura, you have to keep in mind that when you’re attacking and moving, you make yourself pretty visible.
(And in the gnome example, everything you do makes you a damn squeaking toy and some has to stop that squeaking machine!)
So pick whatever race you want. You won’t have any disadvantages or advantages compared to everyone else.