Which is the best cloud storage service for uploading photos?

How would you define best ?

For me, best would be free and ease of access. In that category there are many :

500px

Google Photos

Flickr

Youpic

And many more ….

Google Photos - This is the best when you want to keep your stuff nicely arranged as a private library.

500px - If you are a Pro and want to keep your photos with the best in business. However, you get very little space for free.