Actually the best choice is to store your data with both.
This announcement just made that significantly cheaper, and there's opportunity here for a "cloud RAID" offering to take the hassle out of mirroring one's data. Dropbox already has the API, so they could turn this to their advantage.
I say we support Dropbox for secure storage and dump our images and videos on Google Drive and see how long they store that cheap. Don't just buy a g and throw a few things in there, make them earn this low-balling war.
This announcement just made that significantly cheaper, and there's opportunity here for a "cloud RAID" offering to take the hassle out of mirroring one's data. Dropbox already has the API, so they could turn this to their advantage.