If you only pick one cloud app service, Dropbox is the one you should install. The 2GB of free storage isn’t much, though you can increase that by referring friends. Dropbox offers an app for every major platform, so you can take your files anywhere. It’s also super easy to share files with others.
You can take advantage of alternative cloud services in conjunction with Dropbox to get more free space and separate your files logically. Google Drive offers an impressive 15GB for free, making it another great choice.