Two of the hardest decisions many MMORPG gamers ever face are choosing a race and choosing a class. If you have read the Assassin guide I will assume you have already chosen your class. Aion is based on an epic war story between 3 different Factions, Elyos, Asmodian and Balaur, two of which you can play as. Since you only have two races or factions to choose from, let's look at their background and story first, and then I will talk about the facts you should consider when picking a race for an Assassin.
Elyos are viewed as the divine race; they are visually more warm, friendly, and divine. Once an Elyos becomes a Daevas after their ascension, they will acquire a pair of angelic wings which are visually white to resemble angels in Heaven. The Elyos race inhabit the land of Elysea, which is the lower half of Atreia. Elysea is a rich land filled with plants and fertile lands, which led the Elyos to believe that they are blessed by Aion.
Asmodians have more of an evil or dark appearance, as they closely resemble the Dark Elf race of many other MMORPGs. The Asmodians are brave, hardy, generous, loyal, and are willing to die for the advancement of their Faction. They are not hesitant to give their life for their comrades. Once the Asmodian become a Daeves they will acquire a pair of devilish wings which are a dark, menacing black colour. The Asmodian lives on the opposite end of Elyos in Asmodae, which is the upper part of Atreia. Unlike Elysea, which is inhabited by the Elyos, Asmodae is a cold, icy, and dark land. In order to adapt to the darkness of Asmodae, the Asmodian has developed otherworldly glowing eyes during combat (basically their eyes glow red when they enter into combat).
Sadly one of the major influences involved in choosing a race in Aion is probably going to be your friends. Why? Aion only allows you to play one race per server, so if you play Asmodian on the Server Siel for example, you can not play Elyos and I am sure you would like to play with your friends right? That being said, not everyone is going to be playing Aion with a friend, and there are plenty of opportunities to make friends in-game. So here are some points which you should consider when choosing your race.