I actually use 3 different syncing services: Google Drive, Dropbox and SkyDrive, each with its own specialty.
I use Dropbox for all of my pictures (they recently made a nice improvement on their site which lets you organize with a nice GUI your albums and photos).
I use Google Drive to sync my class notes because it integrates quite usefully with Evernote (using IFTTT). I also manage my personal stuff with Google Drive where I have a 2-step authentication to protect these files.
SkyDrive is mainly used for Excel, Word and PowerPoint files across my work and home computers.