Although World of Warcraft initially launched with only 8 races, the game has grown to include a staggering 23 today. Although 10 of these options, known as "allied races," are more like variants than unique races, they still provide players with the ability to play exactly the character they want. Despite World of Warcraft's player base having so many options available to them, they still tend to gravitate towards a few fan-favorites.
Although Blizzard does usually not provide specific realm population information themselves, there have been multiple different census projects throughout World of Warcraft's history. Since these sources are not official, they cannot provide exact statistics for every realm, but they can still be used as a reliable estimate. Although the numbers used here come from before World of Warcraft: Shadowland's release, the expansion did not include new races, meaning the numbers have likely remained accurate.
The most played race for Alliance players in World of Warcraft are Humans, which make up around 15% of the total characters in the game. Humans have been around since the franchise's first game, Warcraft: Orcs vs Humans, and have been a dominant figure in Azeroth's lore. Human's being so popular in World of Warcraft comes as little surprise, since many players enjoy creating characters who look like themselves and may be uncomfortable playing as a fantasy race.
Night Elves are a close second when it comes to Alliance races in WoW, with an estimated 12% of the class choosing the nocturnal humanoids. Night Elves are an important part of World of Warcraft's lore, playing a crucial role in the War of the Ancients and doing so again during the Third War. Night Elves have a number of qualities that may attract players to select them, including a connection to nature that wasn't shared by the original Alliance races. Since they are also the sole Alliance race with access to the Demon Hunter class in World of Warcraft, it is no surprise that they have remained so popular.
Despite not being added until World of Warcraft: The Burning Crusade, Blood Elves are far and away the most popular race for Horde players. Blood Elves make up just over 15% of the total game's population, over 10% more than the second most popular Horde race, Orcs. Blood Elves possess a number of advantages when compared to the other members of their faction, such as access to both the Demon Hunter and Paladin classes. It is also likely that some Horde players would prefer to play as a more human-like race, making Blood Elves a clear choice.
With how popular Blood Elves have become in World of Warcraft, it is no surprise that the most popular "allied race" is the Void Elves, since they have a similar model. As for the least popular non-allied race, assuming both faction's Pandaren characters are counted as one, then Goblins bring up the rear with just over 2% of the total population.
Although each race in WoW includes passive advantages and unique racial abilities, many players are likely to choose their character based on aesthetics rather than ability. Between Humans, Night Elves, and Blood Elves, it is clear that many of World of Warcraft's players prefer human-like races that have made a major impact on Azeroth's history.