Though Dropbox is more popular with over 45 million users, with 17 million users, Microsoft's SkyDrive is a strong competitor. SkyDrive's most desired feature has been 25GB of free space, much larger than that of most rivals. On Monday, Microsoft revealed its desire to be the "world's hard drive", integrating SkyDrive with Windows 8 to make it easier to access your data from any device.

Source: Yahoo! News