Well, what the 'best game ever' is depends on what you enjoy playing. Assuming you are referring to video games, the most purchased games, their years, the systems they are available on, and about the number of sales they have received are:
Tetris 2006 Mobile, iOS, BlackBerry OS, PlayStation Portable 100 million[1]
Wii Sports 2006 Wii 82.69 million[2]
Minecraft 2009[n 2] Windows, OS X, Linux, Java, Xbox 360, Xbox One, PlayStation 3, PlayStation 4, Mobile, Java applet, Android, iOS, Windows Phone, Amazon Fire TV, Raspberry Pi, PlayStation Vita 70 million[5]
Grand Theft Auto V 2013 PlayStation 3, Xbox 360, PlayStation 4, Xbox One, Windows 54 million[6]
Super Mario Bros. 1985 Nintendo Entertainment System 40.24 million[7]
Mario Kart Wii 2008 Wii 36.38 million[8]
Tetris 1989 Game Boy, Game Boy Color 35 million[9]
Wii Sports Resort 2009 Wii 32.80 million[2]
New Super Mario Bros. 2006 Nintendo DS 30.79 million[10]
Diablo III 2012 Microsoft Windows, OS X, Xbox 360, PlayStation 3 30 million[11][n 3]
Pac-Man 2003 Mobile 30 million[12]
New Super Mario Bros. Wii 2009 Wii 29.32 million[2]
Wii Play 2006 Wii 28.02 million[2]
Grand Theft Auto: San Andreas 2004 PlayStation 2, Microsoft Windows, Xbox, Mac OS X, Xbox 360 27.5 million[13]
Call of Duty: Modern Warfare 3 2011 Microsoft Windows, Xbox 360, PlayStation 3, Wii 26.5 million[14]
Call of Duty: Black Ops 2010 Microsoft Windows, Xbox 360, PlayStation 3, Wii 26.2 million[14]
Grand Theft Auto IV 2008 PlayStation 3, Xbox 360, Microsoft Windows 25 million[15]
Call of Duty: Black Ops II 2012 Windows, Xbox 360, PlayStation 3, Wii U 24.2 million[14]
Kinect Adventures! 2010 Xbox 360 24 million[16]
Nintendogs 2005 Nintendo DS 23.96 million[10]
Pokémon Red, Blue, and Green 1996 Game Boy, Game Boy Color 23.64 million[17][18][19]
Mario Kart DS 2005 Nintendo DS 23.59 million[10]
Pokémon Gold and Silver 1999 Game Boy, Game Boy Color 23 million[20]
Wii Fit 2007 Wii 22.67 million[2]
Call of Duty: Modern Warfare 2 2009 Microsoft Windows, Xbox 360, PlayStation 3 22-29 million[14][21][22]
Wii Fit Plus 2009 Wii 21.11 million[2]
Super Mario World 1990 Super Nintendo Entertainment System 20.6 million[7][23]
Grand Theft Auto: Vice City 2002 Windows, Xbox, PlayStation 2 20 million[24]
The Sims 2 2004 Windows, OS X 20 million[25]
The Elder Scrolls V: Skyrim 2011 Microsoft Windows, PlayStation 3, Xbox 360 20 million[26]
Battlefield 3 2011 Microsoft Windows, Xbox 360, PlayStation 3 20 million[27]
Brain Age 2005 Nintendo DS 19.01 million[10]
Call of Duty: Ghosts 2013 Windows, Xbox 360, Xbox One, PlayStation 3, PlayStation 4, Wii U 19 million[28]
Super Mario Land 1989 Game Boy, Game Boy Color 18.06 million[7]
Super Mario Bros. 3 1988 Nintendo Entertainment System 18 million[29]
Pokémon Diamond and Pearl 2006 Nintendo DS 17.63 million[10]
Grand Theft Auto III 2001 Windows, Xbox, PlayStation 2 17.33 million[24]
Pokémon Ruby and Sapphire 2002 Game Boy Advance 16.22 million
Need for Speed: Most Wanted 2005 PlayStation 2, Xbox, Xbox 360, GameCube, Windows, Game Boy Advance, Nintendo DS 16 million[30]
The Sims 2000 Windows, Mac OS 16 million[31]
Call of Duty 4: Modern Warfare 2007 Windows, Xbox 360, Mac OS X, PlayStation 3, Wii 15.7 million[14]
Call of Duty: World at War 2008 Windows, Xbox 360, PlayStation 3, Wii 15.7 million[14]
Pokémon Black and White 2010 Nintendo DS 15.60 million[10]
Sonic the Hedgehog 1991 Sega Mega Drive/Genesis 15 million[32]
If you were referring to ONLINE games, the list of most played and some info about them are here:
1. LEAGUE OF LEGENDS
The League of Legends is at top position in the list of most popular online games. It is a multiplayer online battle arena video game. The game is developed and released by Roit Games for Microsoft Windows and Mac OSX. League of Legends was released on October 27, 2009.
League of Legends is most popular video game that is played online. According to an estimate the game has 27 million active daily players. About 21.26% online video game players would like to play the League of Legends.
2. WORLD OF WARCRAFT
World of Warcraft (WoW) is created in 2004 by Bizzard Entertainment. It is a massively multiplayer online role-playing game. The game holds the Guinness World Record for the most subscribed massively multiplayer online role-playing game. It has more than 10 million subscribers. It is also the highest grossing video game of all time.
3. DOTA 2
Developed by Valve Corporation, Dota 2 is another most popular online video game. It is also a multiplayer online battle arena video game and was released in July 2013. It was specially developed for Microsoft Windows, OSX and Linux. In our popularity, Dota 2 is at no 3 position. It has become the most actively played game on Steam, with daily peaks of over 800,000 concurrent players.
4. COUNTER-STRIKE: GLOBAL OFFENSIVE
The fourth game of Counter-Strike franchise, Counter-Strike: Global Offensive (CS: GO) is an online first-person shooter game. The game was developed and released by Valve Corporation and Hidden Path Entertainment in August 21, 2012. In terms of popularity, it is one of the most played online games. In 2012 it was the best-selling video game with more than 12 million copies during the year.
5. DIABLO III
Next in category of most popular online games is Diablo III. Diablo III is an action role playing game. It is developed and released by Bizzard Entertainment in 2012 for Microsoft Windows and OS X in 2012. When released in 2012 Diablo III set a new record for fastest-selling PC game by selling 3.5 million copies in the first 24 hours. In 2012 it was the best-selling video game with more than 12 million copies during the year.
6. SMITE
Smite is one of the most played online video game released by Hi-Rez Studios. It is an action Multiplayer Online Battle Arena (MOBA) video game. The game was released for Microsoft Windows and Xbox One in 2014.
7. BATTLEFIELD 4
Released in 2013 Battlefield 4, is another most popular online game developed by Swedish video game developer EA Digital Illusion CE and published by Electronics Arts. It is a first-person shooter video game developed for Microsoft Windows, PlayStation 3, PlayStation 4, Xbox 360 and Xbox One. It is one of the popular video games in the world. According to EA, Battlefield 4 received awards from over 30 video game journalism outlets. These awards included Most Valuable Game Awards and Best Multiplayer Game in 2013.
8. MINECRAFT
A sandbox independent video game Minecraft, is published by the Swedish company Mojang. The game has different versions specially designed for different operating systems like, android, Windows Phone, PlayStatio 4, Xbox One and iOS etc. it one of the popular online games in the world and social sites like facebook, youtube etc. also played significant role in its popularity.
9. WORLD OF TANKS
At No. 9 in our list of most popular online games is the World of Tanks. It is also a massively multiplayer online game. The game is free to play but participants also have the option of playing a free for use of premium features. World of Tanks holds a Guinness World Record in the category of Most Players Online Simultaneously on one MOG Server with over 305,000 users simultaneously in 2013.
10. HEARTHSTONE: HEROES OF WARCRAFT
At No 10 position in the list of top 10 most popular online games is Hearthstone: Heroes of Warcraft. It is a digital collectable card game (CCG). The game is developed by Blizzard Entertainment and released in March 11, 2014. It is a free-to-play with unlimited paid content and limited free content game. The game is available on Microsoft Windows, OS X, iPad, Android tablet and Window 8 touchscreen devices. Hearthstone will be one of the most played online games in next few years. By January 2015, there were than 25 million registered Hearthstone accounts.